isovolumetric

Isovolumetric describes any process in which the volume of the system remains constant. In thermodynamics, an isovolumetric (or isochoric) process is one in which dV = 0; as a result, the system does not perform boundary work (W = ∫ P dV = 0). Heat transfer can occur, leading to a change in internal energy and temperature. For an ideal gas, ΔU = n Cv ΔT, so heating increases internal energy and temperature without changing volume. The pressure generally changes in response to temperature and composition.

In physiology, especially cardiology, the term describes phases of the cardiac cycle where the ventricles are closed and their volume does not change. Isovolumetric contraction follows the closure of the mitral and tricuspid valves; ventricular pressure rises rapidly without a change in volume until the aortic and pulmonary valves open and ejection begins. Isovolumetric relaxation occurs after the aortic and pulmonary valves close and before the atrioventricular valves reopen, during which ventricular pressure falls while volume remains constant. These phases are reflected in pressure–volume relationships and are important for assessing myocardial function and valve performance.

The concept also appears in other contexts as a limiting case or idealization of processes with constrained volume, used in teaching and modeling to separate the effects of pressure and temperature from boundary work.