Table 2.

Physiological vs cardiological systole and diastole

Physiological systole	Cardiological systole
Isovolumic contraction	From M1 to A2, including:
Maximal ejection
	Major part of isovolumic contraction*
	Maximal ejection
	Reduced ejection
Physiological diastole	Cardiological diastole
Reduced ejection	A2 - M1 interval (filling phases included)
Isovolumic relaxation
Filling phases

In Greek, systole means contraction and diastole means "to send apart". Physiological systole lasts from the start of isovolumic contraction to the peak of the ejection phase, so that physiological diastole commences as the LV pressure starts to fall. This concept fits well with the standard pressure-volume curve. Physiological diastole commences as calcium ions are taken up into the SR, so that the myocyte relaxation dominates over contraction and the LV pressure starts to fall as shown on the pressure-volume curve. In contrast, cardiological systole is demarcated by the interval between the first and the second heart sounds, lasting from the first heart sound to the closure of the aortic valve. The remainder of the cardiac cycle automatically becomes cardiological diastole.

* Note that M₁ occurs with a definite albeit short delay after the start of the LV contraction. Modified from Opie LH. Mechanisms of cardiac contraction and relaxation. In: Braunwald E, Zipes DP, Libby P, Bonow RO, eds. Heart Disease. 7^th ed. WB Saunders Company 2005, Chap.19:457-489, page 474.