Phases of the Cardiac Cycle

Phases of the Cardiac Cycle

The cardiac cycle consists of two main phases: diastole and systole.

Diastole

• Early diastole: The heart muscle relaxes, and the heart chambers fill with blood.
• Mid-diastole: The atrioventricular (AV) valves open, allowing blood to flow from the atria to the ventricles.
• Late diastole: The atria contract, pumping additional blood into the ventricles.

Systole

• Isovolumic contraction: The ventricles contract, but the AV valves are closed, and the semilunar valves are closed.
• Rapid ejection: The semilunar valves open, and blood is rapidly ejected from the ventricles into the aorta and pulmonary arteries.
• Reduced ejection: The ventricles continue to contract, but the rate of ejection slows down.

Key Events

• Atrial contraction: The atria contract, pumping additional blood into the ventricles.
• Ventricular contraction: The ventricles contract, pumping blood out of the heart.
• AV valve closure: The AV valves close, preventing backflow from the ventricles to the atria.
• Semilunar valve closure: The semilunar valves close, preventing backflow from the aorta and pulmonary arteries to the ventricles.

Pressure and Volume Changes

• Ventricular pressure: Increases during systole, decreases during diastole.
• Atrial pressure: Decreases during systole, increases during diastole.
• Ventricular volume: Decreases during systole, increases during diastole.
• Atrial volume: Increases during systole, decreases during diastole.

Heart Sounds

• S1 (lub): The sound of the AV valves closing.
• S2 (dub): The sound of the semilunar valves closing.

Phases of the Cardiac Cycle

• The cardiac cycle consists of two main phases: diastole and systole.

Diastole

• Heart muscle relaxes and heart chambers fill with blood during early diastole.
• Atrioventricular (AV) valves open, allowing blood to flow from atria to ventricles during mid-diastole.
• Atria contract, pumping additional blood into ventricles during late diastole.

Systole

• Ventricles contract, but AV valves are closed, and semilunar valves are closed during isovolumic contraction.
• Semilunar valves open, and blood is rapidly ejected from ventricles into aorta and pulmonary arteries during rapid ejection.
• Ventricles continue to contract, but rate of ejection slows down during reduced ejection.

Key Events

• Atrial contraction pumps additional blood into ventricles.
• Ventricular contraction pumps blood out of the heart.
• AV valve closure prevents backflow from ventricles to atria.
• Semilunar valve closure prevents backflow from aorta and pulmonary arteries to ventricles.

Pressure and Volume Changes

• Ventricular pressure increases during systole and decreases during diastole.
• Atrial pressure decreases during systole and increases during diastole.
• Ventricular volume decreases during systole and increases during diastole.
• Atrial volume increases during systole and decreases during diastole.

Heart Sounds

• S1 (lub) is the sound of AV valves closing.
• S2 (dub) is the sound of semilunar valves closing.