Ventricular function

Abstract

The basic cardiac events of Wiggers' cycle (Fig. 1) are: (1) left ventricular (LV) contraction, (2) LV relaxation, and (3) LV filling. A natural starting point is with the arrival of calcium ions at the contractile protein that starts actin-myosin interaction and left ventricular contraction. During the initial phase of contraction, the LV pressure builds up until it exceeds that in the left atrium (normally 10 to 15 mmHg), whereupon the mitral valve closes. With the aortic and mitral valves both shut, the LV volume cannot change and contraction must be isovolumic (iso = the same) until the aortic valve is forced open as the LV pressure exceeds that in the aorta. Once the aortic valve is open, blood is vigorously ejected from the LV into the aorta, which is the phase of maximal or rapid ejection. The speed of ejection of blood is determined both by the pressure gradient across the aortic valve and by the elastic properties of the aorta, which undergoes systolic expansion. © 2006 Humana Press Inc.