(D-L) Nebivolol is a new beta 1-selective adrenoceptor blocker which in normal individuals preserves rest and exercise hemodynamics. We assessed the effects of the enantiomers (L- and D-nebivolol) on left ventricular (LV) systolic and diastolic function and compared their effects with those of the racemic mixture. LV angiography (+Millar) was performed before and after intravenous (i.v.) infusion of either D- or L-nebivolol (1.25-2.5 mg, n = 22) in patients with ischemic heart disease and previous myocardial infarction. Neither L- nor D-nebivolol produced significant changes in heart rate (HR), peak (+) dP/dt, (dP/dt) DP40, cardiac index (CI) or ejection fraction (EF). Diastolic distensibility, evaluated from the shift of the pressure-volume data at the time of mitral valve opening, did not improve after D- or L-enantiomers administration. In contrast, both D-L-nebivolol 2.5 mg (n = 9) and atenolol 15 mg (n = 9) significantly reduced HR and peak (+) dP/dt, but in comparison to atenolol D-L nebivolol improved EF (+4% after D-L nebivolol vs. -4% after atenolol; p < 0.05 D-L nebivolol vs. atenolol) and maintained cardiac output CO, (+2% vs. -21%; p < 0.05 between groups). Moreover, unlike any of the other drugs in the study, the racemate shifted the diastolic pressure-volume data downward, suggesting improved LV distensibility. The beneficial effects of nebivolol on LV systolic and diastolic function appears to require the presence of both D- and L-enantiomers.