isovolumic relaxation

i·so·vol·u·mic re·lax·a·tion

that part of the cardiac cycle between the time of aortic valve closure and mitral opening, during which the ventricular muscle decreases its tension without lengthening so that ventricular volume remains unaltered; the heart is never precisely isovolumetric (vs. isovolumic) except during long diastoles with a midiastolic period of diastasis. Synonym(s): isovolumetric relaxation