This is due to a very definite influence upon the different portions of the cardiac cycle.
cardiac cycle n.
A complete beat of the heart, including systole and diastole and the intervals between, beginning with any event in the heart's action to the moment when that same event is repeated.
|cardiac cycle |
The rhythmic contraction (systole) and relaxation (diastole) of the chambers of the heart that corresponds to one heartbeat. During the cardiac cycle, blood is pumped out of the heart into the aorta and the pulmonary artery, and blood reenters the heart from the venae cavae and the pulmonary veins. The heart's valves open and close in response to pressure differences between the chambers.