Phases of the Cardiac Cycle

Phases of the Cardiac Cycle

Diastole

• The heart is relaxed and fills with blood
• Atrioventricular (AV) valves open, allowing blood to flow from atria to ventricles
• Semilunar valves closed, preventing backflow into pulmonary and aortic trunks

Atrial Contraction

• Atria contract, pumping blood into ventricles
• AV valves still open, allowing blood to flow into ventricles
• Semilunar valves remain closed

Ventricular Contraction (Systole)

• Ventricles contract, pumping blood out of the heart
• AV valves close, preventing backflow into atria
• Semilunar valves open, allowing blood to flow into pulmonary and aortic trunks

Isovolumic Contraction

• Ventricles contract, but semilunar valves remain closed
• Blood volume in ventricles decreases, but no blood is ejected

Rapid Ejection

• Semilunar valves open, allowing blood to flow out of ventricles and into pulmonary and aortic trunks
• Blood pressure increases

Reduced Ejection

• Blood flow out of ventricles slows down
• Blood pressure decreases

Isovolumic Relaxation

• Ventricles relax, and semilunar valves close
• Blood volume in ventricles increases, but no blood flows in

Other Key Concepts

• Stroke Volume (SV): volume of blood ejected per beat
• Cardiac Output (CO): total volume of blood pumped per minute (CO = SV x Heart Rate)
• End-Diastolic Volume (EDV): volume of blood in ventricles at end of diastole
• End-Systolic Volume (ESV): volume of blood in ventricles at end of systole

Phases of the Cardiac Cycle

Diastole

• Heart is relaxed and fills with blood
• Atrioventricular (AV) valves are open, allowing blood to flow from atria to ventricles
• Semilunar valves are closed, preventing backflow into pulmonary and aortic trunks

Atrial Contraction

• Atria contract, pumping blood into ventricles
• AV valves are still open, allowing blood to flow into ventricles
• Semilunar valves remain closed

Ventricular Contraction (Systole)

• Ventricles contract, pumping blood out of the heart
• AV valves are closed, preventing backflow into atria
• Semilunar valves are open, allowing blood to flow into pulmonary and aortic trunks

Isovolumic Contraction and Relaxation

• Ventricles contract, but semilunar valves remain closed, and blood volume in ventricles decreases
• Ventricles relax, and semilunar valves close, and blood volume in ventricles increases

Blood Flow and Pressure

• Blood flow out of ventricles increases, and blood pressure increases during rapid ejection
• Blood flow out of ventricles slows down, and blood pressure decreases during reduced ejection

Key Concepts

Cardiac Output and Stroke Volume

• Stroke Volume (SV) is the volume of blood ejected per beat
• Cardiac Output (CO) is the total volume of blood pumped per minute, calculated by CO = SV x Heart Rate

Ventricular Volumes

• End-Diastolic Volume (EDV) is the volume of blood in ventricles at the end of diastole
• End-Systolic Volume (ESV) is the volume of blood in ventricles at the end of systole