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Questions and Answers
Which phase of the cardiac cycle involves the closure of the mitral valve to the closure of the aortic valve?
Which phase of the cardiac cycle involves the closure of the mitral valve to the closure of the aortic valve?
What happens immediately after the QRS complex during the cardiac cycle?
What happens immediately after the QRS complex during the cardiac cycle?
LaPlace's Law indicates that an increase in wall tension leads to what effect on pressure?
LaPlace's Law indicates that an increase in wall tension leads to what effect on pressure?
The P-wave of the ECG corresponds to which event in the cardiac cycle?
The P-wave of the ECG corresponds to which event in the cardiac cycle?
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During which phase of the cardiac cycle does the heart relax and the pressure drops despite no open valves?
During which phase of the cardiac cycle does the heart relax and the pressure drops despite no open valves?
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What is the purpose of the Wiggers' Diagram in understanding the cardiac cycle?
What is the purpose of the Wiggers' Diagram in understanding the cardiac cycle?
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What event closely follows the closure of the aortic valve?
What event closely follows the closure of the aortic valve?
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What initiates the contraction phase according to the explanation of cardiac function?
What initiates the contraction phase according to the explanation of cardiac function?
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In the context of LaPlace's Law, what aspect does the thickness of the wall influence?
In the context of LaPlace's Law, what aspect does the thickness of the wall influence?
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What is the primary role of myosin ATPase in the heart?
What is the primary role of myosin ATPase in the heart?
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Which equation correctly represents cardiac output (CO)?
Which equation correctly represents cardiac output (CO)?
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What is the E-wave flow on transmitral Doppler echocardiography primarily associated with?
What is the E-wave flow on transmitral Doppler echocardiography primarily associated with?
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How does ATP influence cardiac muscle relaxation?
How does ATP influence cardiac muscle relaxation?
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What is represented by the area of the PV loop in cardiac physiology?
What is represented by the area of the PV loop in cardiac physiology?
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Which heart sound is associated with the closure of the aortic valve?
Which heart sound is associated with the closure of the aortic valve?
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Which statement best describes the End Diastolic Pressure Volume Relationship (EDPVR)?
Which statement best describes the End Diastolic Pressure Volume Relationship (EDPVR)?
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What effect does increasing afterload have on the timing of aortic valve opening?
What effect does increasing afterload have on the timing of aortic valve opening?
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Fick's Method quantifies oxygen utilization based on which factors?
Fick's Method quantifies oxygen utilization based on which factors?
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What is the relationship between end diastolic volume (EDV) and stroke volume (SV)?
What is the relationship between end diastolic volume (EDV) and stroke volume (SV)?
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Which of the following is NOT a step in the sequence of cardiac function outlined in the lectures?
Which of the following is NOT a step in the sequence of cardiac function outlined in the lectures?
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Which statement accurately describes the left and right ventricles during systole?
Which statement accurately describes the left and right ventricles during systole?
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What happens to energy sources in the heart when ATP levels decrease?
What happens to energy sources in the heart when ATP levels decrease?
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What happens to the ejection fraction (EF) when preload is increased?
What happens to the ejection fraction (EF) when preload is increased?
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Which factor is primarily responsible for the heart's higher oxygen utilization compared to the brain?
Which factor is primarily responsible for the heart's higher oxygen utilization compared to the brain?
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Which heart sound occurs during the early rapid filling phase?
Which heart sound occurs during the early rapid filling phase?
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What can reduce the contractility of the heart muscle?
What can reduce the contractility of the heart muscle?
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What is the significance of gap junctions in myocytes?
What is the significance of gap junctions in myocytes?
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During which phase of the cardiac cycle is diastasis observed?
During which phase of the cardiac cycle is diastasis observed?
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What effect does a dysfunctional heart have on length-dependent activation?
What effect does a dysfunctional heart have on length-dependent activation?
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Which factor most significantly influences the pressure generated by the heart according to LaPlace's Law?
Which factor most significantly influences the pressure generated by the heart according to LaPlace's Law?
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In the context of the heart's structure, how does an increase in wall tension affect cardiac output?
In the context of the heart's structure, how does an increase in wall tension affect cardiac output?
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What is the primary purpose of examining the Wiggers' Diagram in relation to cardiac function?
What is the primary purpose of examining the Wiggers' Diagram in relation to cardiac function?
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How does the Frank-Starling relationship explain changes in cardiac output with respect to preload?
How does the Frank-Starling relationship explain changes in cardiac output with respect to preload?
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According to LaPlace's Law, which of the following scenarios would result in the least pressure generation by the heart?
According to LaPlace's Law, which of the following scenarios would result in the least pressure generation by the heart?
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What is typically observed in patients with dilated cardiomyopathies regarding cardiac function?
What is typically observed in patients with dilated cardiomyopathies regarding cardiac function?
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In assessing cardiac function, which of the following is an implication of the relationship between preload and length-dependent activation?
In assessing cardiac function, which of the following is an implication of the relationship between preload and length-dependent activation?
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What role do valves play in the heart's ability to generate pressure?
What role do valves play in the heart's ability to generate pressure?
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What component of diastolic function is primarily associated with the process of early filling of the heart?
What component of diastolic function is primarily associated with the process of early filling of the heart?
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What cardiac function is most affected by the relationship described in the Frank-Starling mechanism?
What cardiac function is most affected by the relationship described in the Frank-Starling mechanism?
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Which of the following is the primary consumer of oxygen in cardiac cells?
Which of the following is the primary consumer of oxygen in cardiac cells?
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Which mechanism enables the movement of myocytes to be coordinated with respect to contraction?
Which mechanism enables the movement of myocytes to be coordinated with respect to contraction?
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In relation to cardiac output, what is the likely result of increased afterload?
In relation to cardiac output, what is the likely result of increased afterload?
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What occurs during isovolumic contraction in the cardiac cycle?
What occurs during isovolumic contraction in the cardiac cycle?
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How does wall thickness influence the wall stress according to LaPlace's law?
How does wall thickness influence the wall stress according to LaPlace's law?
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What is indicated by the P-wave on an ECG?
What is indicated by the P-wave on an ECG?
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During which phase does the left ventricle begin to fill after contraction?
During which phase does the left ventricle begin to fill after contraction?
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What occurs immediately after the aortic valve closes in the cardiac cycle?
What occurs immediately after the aortic valve closes in the cardiac cycle?
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What does the QRS complex represent in the cardiac cycle?
What does the QRS complex represent in the cardiac cycle?
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Which of the following describes the state of blood flow during the ejection phase?
Which of the following describes the state of blood flow during the ejection phase?
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During which part of the cardiac cycle does the left ventricle's pressure drop below atrial pressure?
During which part of the cardiac cycle does the left ventricle's pressure drop below atrial pressure?
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What is the relationship between action potentials and ventricular contraction?
What is the relationship between action potentials and ventricular contraction?
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What occurs to the heart during the rapid filling phase?
What occurs to the heart during the rapid filling phase?
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What is the primary impact of increased preload on stroke volume according to the Frank-Starling mechanism?
What is the primary impact of increased preload on stroke volume according to the Frank-Starling mechanism?
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Which factor is least likely to contribute to increased inotropy?
Which factor is least likely to contribute to increased inotropy?
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How does a dysfunctional heart differ from a normal heart in terms of myocardial contractility?
How does a dysfunctional heart differ from a normal heart in terms of myocardial contractility?
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What do the pressure-volume loops of a heart under low calcium conditions demonstrate?
What do the pressure-volume loops of a heart under low calcium conditions demonstrate?
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In terms of oxygen consumption, how does heavy exercise change the MVO2 in the heart?
In terms of oxygen consumption, how does heavy exercise change the MVO2 in the heart?
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How does passive stiffness relate to the end diastolic pressure-volume relationship in the context of cardiac function?
How does passive stiffness relate to the end diastolic pressure-volume relationship in the context of cardiac function?
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What effect does increased inotropy have on stroke volume during cardiac function?
What effect does increased inotropy have on stroke volume during cardiac function?
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In a pressure-volume diagram, how would a heart in heart failure appear compared to a healthy heart?
In a pressure-volume diagram, how would a heart in heart failure appear compared to a healthy heart?
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What happens to myocardial tension generation as sarcomere length increases in healthy myocardial tissue?
What happens to myocardial tension generation as sarcomere length increases in healthy myocardial tissue?
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What is the primary characteristic of the early rapid filling phase of the cardiac cycle?
What is the primary characteristic of the early rapid filling phase of the cardiac cycle?
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During which phase does the late atrial filling occur?
During which phase does the late atrial filling occur?
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What defines systole and diastole in the context of the cardiac cycle?
What defines systole and diastole in the context of the cardiac cycle?
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What wave is associated with early rapid filling in the cardiac cycle?
What wave is associated with early rapid filling in the cardiac cycle?
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What happens to diastasis as heart rate increases?
What happens to diastasis as heart rate increases?
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The A-wave occurs during which specific actions of the heart?
The A-wave occurs during which specific actions of the heart?
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What phase is indicated just before the E-wave in a typical cardiac cycle representation?
What phase is indicated just before the E-wave in a typical cardiac cycle representation?
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What impact does an earlier firing P-wave have during exercise?
What impact does an earlier firing P-wave have during exercise?
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Which statement accurately describes the relationship of E and A waves in terms of cardiac cycle timing?
Which statement accurately describes the relationship of E and A waves in terms of cardiac cycle timing?
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What phase immediately correlates with the contraction and ejection categorized as systole?
What phase immediately correlates with the contraction and ejection categorized as systole?
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Study Notes
LaPlace's Law
- Relates pressure within a sphere to wall stress.
- Equation: Wall stress (σ) = Pressure (P) * Radius (r) / Thickness (u).
- Increased wall tension corresponds to increased pressure, like inflating a balloon.
Wiggers' Diagram
- Illustrates the sequence of events in the cardiac cycle by linking pressure and volume (or flow) changes.
- Starts with action potentials triggering contraction (Excitation-Contraction Coupling).
- Contraction increases tension, leading to increased pressure via LaPlace's Law.
Phases of the Cardiac Cycle
Systole
- Mitral valve closure to aortic valve closure.
- Contraction and ejection of blood.
Diastole
- Aortic valve closure to mitral valve closure.
- Relaxation and filling of the heart.
ECG Correlation with Ventricular Events
-
P-wave: Atrial depolarization and contraction.
- Represents atrial contraction and filling of the ventricle.
- There's a delay between the P-wave and changes in flow due to excitation-contraction coupling.
-
QRS complex: Ventricular depolarization and contraction.
- Ventricular pressure rises, closing the mitral valve.
- All valves are closed during the isovolumic contraction phase.
- There's a delay between the QRS complex and mitral valve closure.
-
Ventricular Ejection: LV pressure exceeds aortic pressure, opening the aortic valve.
- Blood leaves the heart, reducing its volume.
- Isovolumic Relaxation: Aortic valve closes as the heart relaxes, pressure falls despite no open valves.
-
Early Rapid Filling: LV pressure drops below atrial pressure, opening the mitral valve.
- Rapid filling of the heart begins.
- E-wave on transmitral Doppler echocardiography.
- Diastasis: A period of "rest" with minimal flow when the heart rate is slow.
-
Late Atrial Filling (Atrial Systole): A new P-wave occurs, causing additional atrial filling.
- A-wave on transmitral Doppler echocardiography.
Right vs Left Ventricle
- RV wall is thinner than LV wall.
- RV generates less pressure than LV.
- Peak RV pressure ~25 mmHg.
- Peak LV pressure ~120 mmHg.
- RV and LV contract at slightly different times, usually with some overlap.
Auscultation
- Listening to body sounds.
- Common sounds: heart, lung, pulse pressure.
Heart Sounds
- Generated by valve closures and blood deceleration.
- 1st heart sound: Mitral valve closure/aortic valve opening ("Lub").
- 2nd heart sound: Aortic valve closure/mitral valve opening ("Dub").
- 3rd heart sound: Blood deceleration during early rapid filling.
- 4th heart sound: Blood deceleration during late atrial filling.
Splitting of Heart Sounds
- Normally, sounds from the left and right ventricles overlap.
- If RV doesn't close the pulmonary valve at the same time the LV closes the aortic valve, the 2nd heart sound may "Split".
- A2, P2 for an aortic and pulmonary sound.
Pressure-Volume Loop
- Traces the cardiac cycle in a counter-clockwise direction.
- "Corners" defined by valve closures.
Important Measurements and Indexes
- EDV (End Diastolic Volume): Volume of blood when mitral valve closes.
- ESV (End Systolic Volume): Volume of blood in the heart when aortic valve closes.
- SV (Stroke Volume): Difference between EDV and ESV.
-
EF (Ejection Fraction): Percentage of blood ejected, (100 * SV / EDV) or (100 * (EDV - ESV) / EDV).
- Normal EF is >50%.
Afterload, Preload, and Contractility
- Changing afterload (systemic/aortic blood pressure) alters aortic valve opening but not mitral valve closure (preload).
- Afterload impacts aortic valve closure/ESV and allows calculation of contractility or inotropy.
- Connecting end-systolic points with different afterloads creates a line whose slope indicates contractility.
Factors Reducing Contractility
- Reduced calcium release from the sarcoplasmic reticulum.
- Decreased thin filament activation.
- Slowed or inhibited myosin ATPase.
Preload and Frank-Starling Law
- Increased preload generally leads to increased stroke volume.
- Frank-Starling Law: Myocytes contract more vigorously at longer lengths/higher volumes.
- Length-dependent activation can be broken in a sick heart, leading to reduced EF.
Pressure-Volume Loops Reflecting Heart Function
- Normal Heart: Myocardium generates more tension at longer lengths, leading to increased stroke volume.
- Dysfunctional Heart: Myocardium generates the same force at all lengths, limiting contractility and reducing EF.
Energy Utilization by the Heart
- Requires significant energy, using oxygen for mitochondrial respiration.
- Myosin ATPase is a primary ATP user, requiring a shift from fatty acid to glucose utilization when ATP availability is reduced.
- ATP is crucial for relaxation as it detaches the myosin from the rigor state. Reduced ATP impairs relaxation.
Work of the Heart
- Work is the effort used to move blood out of the left ventricle.
- Work = Area of the Pressure-Volume loop, approximated as a rectangle.
- Top = Mean Arterial Pressure (MAP).
- Bottom = Diastolic Pressure.
- Work = Stroke Volume x (MAP - Diastolic Pressure).
Fick's Method
- Gold standard for quantifying oxygen utilization.
- CO (Cardiac Output) = O2 Uptake (ml O2/min) / A-V O2 Difference (ml O2/L blood).
- Represents the rate of oxygen consumption divided by the difference between arterial and venous oxygen content.
- Relates oxygen use to cardiac output - the amount of blood pumped through the body.
Cardiac Output
- Represents blood delivered to the body.
- Calculated as: CO = SV x HR (Heart Rate).
Sequence of Events in Cardiac Function
- Myocyte action potential driven by sodium, potassium, etc.
- Excitation spreads via gap junctions.
- Electrocardiogram tracks depolarization.
- Calcium-induced calcium release by RyR increases cytosolic calcium.
- Increased cytosolic calcium allows troponin/tropomyosin movement, enabling myosin binding.
- Myosin ATPase generates force.
- Cardiac structure transmits force into pressure.
- Cardiac output is generated, influenced by all prior steps.
Laplace’s Law
- Laplace’s Law describes the relationship between pressure, wall tension, radius, and thickness of a sphere.
- The heart can be approximated as a sphere.
- A larger radius requires less pressure to be generated.
- Laplace's Law can be used to understand dilated cardiomyopathies and hypertension.
Wiggers’ Diagram
- Wiggers’ Diagram describes the relationship between the electrocardiogram (ECG), ventricular pressure, volume, and valve activity during the cardiac cycle.
- The P-wave corresponds to atrial depolarization and contraction, resulting in atrial filling of the ventricle.
- The QRS complex corresponds to ventricular depolarization and contraction, causing ventricular pressure to rise and close the mitral valve, resulting in isovolumic contraction.
- When the ventricular pressure exceeds aortic pressure, the aortic valve opens, allowing blood to exit the ventricle and reducing its volume (ejection).
- As contraction fades and the heart relaxes, the aortic valve closes, leading to a decrease in pressure despite closed valves (isovolumic relaxation).
- Once ventricular pressure falls below atrial pressure, the mitral valve opens, allowing for rapid filling of the ventricle (early rapid filling).
- Diastasis is a period of low blood flow during periods of slow heart rate, occurring following early rapid filling.
- Late atrial filling or atrial systole occurs following diastasis, when a new P-wave causes further atrial filling.
- Systole refers to ventricular contraction and ejection, while diastole refers to ventricular relaxation and filling.
Pressure-Volume Relationships
- Frank-Starling Mechanism: A larger preload (end-diastolic volume, end-diastolic pressure, or right atrial pressure) results in a larger stroke volume.
- Length Dependent Activation: The relationship between sarcomere length and muscle tension, explaining how increasing preload can increase contractility.
- Inotropy: Increased inotropy (contractility) leads to a greater increase in stroke volume.
- Myosin ATPase: Is the primary consumer of ATP in the heart, and, therefore, the primary driver of oxygen consumption by the heart.
- Diastolic Function: Refers to the ability of the heart to relax and fill.
- Diastolic Dysfunction: Is now more common than systolic dysfunction and relates to the heart’s ability to relax and fill passively.
Cardiac Output
- Cardiac Output (CO) is the amount of blood pumped by the heart per minute. It can be calculated using Fick’s method or by multiplying stroke volume (SV) and heart rate (HR): CO = SV * HR.
Final Integration
- Cardiac Function. Cardiac function is a complex interplay of various cellular and structural mechanisms.
- L6 (Myocyte Action Potential): The myocyte action potential is initiated by sodium influx, followed by potassium efflux, and is propagated via gap junctions.
- L7 (Electrocardiogram): The electrocardiogram tracks the path of depolarization across the heart.
- L8 (Calcium-Induced Calcium Release): Calcium-induced calcium released by the ryanodine receptor (RyR) causes an increase in cytosolic calcium.
- L9 (Cardiac Structure): Cardiac structure helps to transmit force (tension/stress) into pressure.
- Integration of Concepts: The integration of action potential, calcium dynamics, muscle contraction, and cardiac structure creates the heart’s ability to generate and control cardiac output.
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Description
Test your understanding of LaPlace's Law and the phases of the cardiac cycle. This quiz covers the relationship between pressure, wall stress, and the dynamics of the heart during systole and diastole. Additionally, it explores the correlation of ECG readings with ventricular events for a comprehensive overview.
