The effect on myocardial contractility of a new beta-adrenergic receptor blocking drug, penbutolol

1 The inotropic effect of penbutolol, a new beta-adrenergic receptor blocking drug, has been compared with that of propranolol in two similar groups of six subjects each. 2 Inotropic changes were assessed from changes in myocardial contractility index [LV dp-dt/11 T] as well as the slope of the regression line relating LV dp/dt to LVED during incremental pacing. 3 Penbutolol was found to have a significant negative inotropic effect of an order similar to that of propranolol in the respective doses studied.