Effect of sodium nitroprusside on myocardial performance and venous tone.

The action of sodium nitroprusside upon the mechanical performance of the isolated, working rat heart and on isolated bull veins has been studied. Cumulative concentrations of 1--1000 ng sodium nitroprusside per ml had no effect on left ventricular pressure, end-diastolic left ventricular pressure, dp/dtmax, cardiac output and calculated wall stiffness of isolated rat hearts with constant rate, preload and afterload. Isolated strips of bull veins contracted with noradrenaline showed a dose dependent relaxation by sodium nitroprusside in concentrations of 5--1000 ng per ml. This study shows that sodium nitroprusside has no direct effect on myocardial contractility and causes venous relaxation.