Phases of the Cardiac Cycle

Author: Scott A. Sheffield MS

Last update:

Phases of the Cardiac Cycle:

The cardiac cycle is the sequence of events that occur in the heart with each beat. In this cycle, blood is pumped out of the heart and oxygen is circulated around the body.

  1. As the ventricles relax from the previous cycle, blood image descriptionpassively flows into the ventricles from the atria through the open atrioventricular (AV) valves.
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Blood passively flowing into the ventricles from the atria.
  1. Both image descriptionatria contract (atria systole) to forcibly fill the ventricles with blood.
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Atria contracting and forcibly filling the ventricles with blood.
  1. The image descriptionventricles begin to contract (ventricular systole) after they are filled, which increases the intraventricular pressure. In response, the AV valves move upward and block blood from flowing back into the relaxing atria.

Keep learning the anatomy of the heart with this comprehensive heart revision guide.

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The ventricles contracting and the AV valves moving upward.
  1. The image descriptionsemilunar valves open due to continued ventricular contraction and rising intraventricular pressure. Blood enters the aorta and pulmonary trunk arteries and is then distributed through-out the body.
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The semilunar valves open and blood enters the aorta and pulmonary trunk arteries.
  1. After they contract, the ventricles enter a period of relaxation (ventricular diastole). The intraventricular pressure drops and blood in the large arteries reverses flow. This forces the image descriptionsemilunar valves to close, which prevents blood from entering the ventricles.
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Blood in the large arteries reverses flow, forcing the semilunar valves to close.
  1. The drop in ventricular pressure also allows the AV valves to re-open and a image descriptionnew cycle begins.
Movement of the heart valves animation slide 1
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The cardiac cycle beginning anew.
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