Cardiac cycle

Definition

The cardiac cycle is the sequence of events that occur in the heart from the beginning of one heartbeat to the next. It includes both systole (contraction) and diastole (relaxation) phases.

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 of the heart.
3. During diastole, the heart's ventricles relax and fill with blood from the atria.
4. The cardiac cycle is regulated by electrical impulses that originate in the sinoatrial (SA) node.
5. A complete cardiac cycle typically lasts about 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 usually last in a healthy adult at rest?
• What part of the heart regulates the electrical impulses that control the cardiac cycle?

Related terms

Systole:

The phase of the cardiac cycle during which the ventricles contract and pump blood.

Diastole:

The phase of the cardiac cycle during which the ventricles relax and fill with blood.

Sinoatrial (SA) Node:

A group of cells located in the right atrium that generate electrical impulses to regulate heartbeat.