(1) the maximum rate of an enzyme-catalyzed reaction that can be achieved by progressively increasing the substrate concentration at a given enzyme concentration; in cases of substrate inhibition, Vmax is an extrapolated value in the absence of such inhibition; Cf.: Michaelis-Menten equation (2) the maximum initial rate of shortening of a myocardial fiber that can be obtained under zero load; used to evaluate the contractility of the fiber.