What is Cardiac Cycle?

The Cardiac cycle is the performance of the human heart from the ending of one heartbeat to the beginning of the next. A single cycle of cardiac activity can be divided into two basic phases – diastole and systole. one during which the heart muscle relaxes and refills with blood, called diastole, following a period of robust contraction and pumping of blood, dubbed systole. Assuming a healthy heart and a typical rate of 70 to 75 beats per minute. The cardiac cycle begins with the atrium and ventricle in a relaxed state.

Cardiac Cycle Phases

  • Atrial Diastole: In this stage, chambers of the heart are calmed. That is when the aortic valve and pulmonary artery closes and atrioventricular valves open, thus causing chambers of the heart to relax.
  • Atrial Systole: At this phase, blood cells flow from atrium to ventricle, and at this period, atrium contracts.
  • Isovolumic Contraction: At this stage, ventricles begin to contract. The atrioventricular valves, valve, and pulmonary artery valves close, but there won’t be any transformation in volume.
  • Ventricular Ejection: Here ventricles contract and emptying. Pulmonary artery and aortic valve close.
  • Isovolumic Relaxation: In this phase, no blood enters the ventricles, and consequently, pressure decreases, ventricles stop contracting and begin to relax. Now due to the pressure in the aorta – pulmonary artery and aortic valve close.
  • Ventricular Filling Stage: In this stage, blood flows from atria into the ventricles. It is altogether known as one stage (first and second stage). After that, they are three phases that involve the flow of blood to the pulmonary artery from ventricles.

Cardiac Cycle

Duration of Cardiac Cycle

In a normal person, a heartbeat is 72 beats/minute. So, the duration of one cardiac cycle can be calculated as:
1/72 beats/minute=.0139 minutes/beat
At a heartbeat 72 beats/minute, the duration of each cardiac cycle will be 0.8 seconds.

  • Atrial systole: Continues for about 0.1 seconds.
  • Ventricular systole: Continues for about 0.3 seconds.
  • Atrial diastole: Continues for about 0.7 seconds.
  • Ventricular diastole: Continues for about 0.5 seconds.

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