heart isovolumetric relaxation time left ventricular isovolumetric relaxation time 2014-08-06T10:31:27Z JSMITH LV-IVRT The length of time in the cardiac cycle between the end of left ventricular relaxation and the start of left ventricular filling. This represents the time in the cardiac cycle between closure of the aortic valve and opening of the mitral valve. time constant of isovolumetric LV fall