The acute hemodynamic effects of intravenous acebutolol, 50 mg, and propranolol, 10 mg, were evaluated in 12 patients undergoing diagnostic cardiac catheterization. Each patient received acebutolol or propranolol according to a list of randomization. Both acebutolol and propranolol depressed left ventricular function. There was a significant increase in left ventricular end-diastolic pressure at rest and after isometric exercise, with a concomitant decrease in cardiac index. Systemic vascular resistance was increased by both drugs. The increment after patients received acebutolol was not statistically significant; however, with propranolol it was statistically significant. The overall hemodynamic effects of acebutolol and propranolol are similar, but a quantitative difference exists in their effect on systemic vascular resistance. Acebutolol, a cardioselective agent, produces less of a peripheral vascular beta 2-blockade than does propranolol.