Cardiac cycle

Definition

The cardiac cycle is the sequence of events that occurs during one heartbeat. It includes the phases of diastole (relaxation) and systole (contraction) in the atria and ventricles.

5 Must Know Facts For Your Next Test

1. The cardiac cycle consists of two main phases: systole and diastole.
2. During systole, the heart's ventricles contract to pump blood out to the lungs and body.
3. Diastole involves relaxation of the heart muscles, allowing the chambers to fill with blood.
4. The SA node initiates the electrical impulses that regulate the timing of the cardiac cycle.
5. Each complete cardiac cycle takes approximately 0.8 seconds in a healthy adult at rest.

Review Questions

• What are the two main phases of the cardiac cycle?
• How long does a complete cardiac cycle typically take in a healthy adult?
• Which part of the heart generates electrical impulses to control the timing of the cardiac cycle?

Related terms

Systole: The phase of the cardiac cycle when heart muscles contract to pump blood.

Diastole: The phase of relaxation in the cardiac cycle when heart chambers fill with blood.

SA Node: The sinoatrial node, which acts as the natural pacemaker of the heart by initiating electrical impulses.