The cardiac cycle describes the coordinated and rhythmic series of muscular contractions associated with the normal heart beat.

The cardiac cycle can be subdivided into two major phases, the systolic phase and the diastolic phase. Systole occurs when the ventricles of the heart contract. Accordingly, systole results in the highest pressures within the systemic and pulmonary circulatory systems. Diastole is the period between ventricular contractions when the right and left ventricles relax and fill.

The cardiac cycle cannot be described as a linear series of events associated with the flow of blood through the four chambers. One can not accurately describe the cardiac cycle by simply tracing the path of blood from the right atrium, into the right ventricle, into the pulmonary circulation, the venous pulmonary return to the left atrium, and finally the ejection into the aorta and systemic circulation by the contraction of the...