The Cardiac Cycle

To understand the cardiac cycle, the motion of the valves and the pressures within the chambers should be reviewed. The interrelationships of valve motion are critically important and must be understood. Only with the knowledge of these cycles can the clinician fully comprehend the cardiac physical examination and heart sounds. The pressure tracings and valve motions are shown in Figure 14-6.

Normally, only the closing of the heart valves can be heard. The closure of the atrioventricular valves, the tricuspid and the mitral, produces the first heart sound (S1). The closure of the semilunar valves, the aortic and the pulmonic, produces the second heart sound (S2).

The opening of the valves can be heard only if they are damaged. When an atrioventricular valve is narrowed, or stenotic, the opening of the valve may be heard and is termed an opening snap. If a semilunar valve is stenotic, the opening may be heard and is termed an ejection click. It should be noted that in Figure 14-6, the term opening snap refers to the opening of a pathologically damaged atrioventricular valve that occurs during diastole, and the term ejection click refers to the opening of a damaged semilunar valve that occurs during systole.

The sequence of the opening and closing of the four valves is as follows:

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