In cardiac physiology, isovolumetric contraction is an event occurring in early systole during which the ventricles contract with no volume change (isovolumetrically). This short-lasting portion of their contraction takes place during a moment when the heart valves are all closed.
In a healthy young adult, blood enters the atria and flows to the ventricles via the opened atrioventricular valves (tricuspid and mitral valves). Atrial contraction rapidly follows, actively pumping about 20% of the returning blood. As diastole ends, the ventricles start depolarizing and, while ventricular pressure starts to rise owing to contraction, the atrioventricular valves close, so as to prevent backflow to the atria. At this stage, which corresponds to the R peak or the QRS complex seen on an ECG, the semilunar vales (aortic and pulmonary valves) are also closed. The net result is that, while contraction causes ventricular pressures to rise sharply, there is no overall change in volume because of the closed valves. The isovolumetric contraction lasts about 0.03 s, but this short period of time is enough to build up a sufficiently high pressure that eventually overcomes that of the aorta and the pulmonary trunk upon opening of the semilunar valves, therefore allowing the correct unidirectional flow of blood.
The word contains the prefix iso-, derived from the Ancient Greek ἴσος (ísos), meaning equal. Therefore, an isovolumetric contraction is one in which the volume of fluid remains constant.
- Pocock, J., and Richards, C.D. (2006). Human Physiology, the basis of Medicine (3rd edition), pp. 274–275, Oxford University Press, Oxford