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

Learn about the different stages of the cardiac cycle, including diastole, atrial contraction, and ventricular contraction. Understand the role of AV valves and semilunar valves in the heart's pumping process.