In a subacute experiment the authors studied the effects of a fourteen -day treatment with nebivolol, 5 mg once a day, in 10 healthy male volunteers with a mean age of thirty-one, twenty-five to thirty-nine years, by comparing the results of the resting ratio of the preejection period (PEP) to the left ventricular ejection time (LVET), as measured by systolic time intervals (STI), with the results obtained by equilibrium radionuclide angiocardiography (ERNA), using technetium 99m-labeled autologous red blood cells as a marker. A submaximal treadmill exercise test performed before and during treatment demonstrated that nebivolol significantly (p less than 0.01) reduced peak exercise heart rate and systolic blood pressure from a mean value of 158 +/- 5.4 bpm to 131 +/- 4.3 bpm and from 171 +/- 4.9 mmHg to 144 +/- 4.5 mmHg respectively. The data from the STI and ERNA were calculated and analyzed independently by two observers. A highly significant (r = 0.8182, p = 0.0038) correlation was found between the changes of stroke volume (SV) and PEPc/LVETc during treatment with nebivolol. Furthermore end-diastolic volume significantly(p = 0.03) increased from a mean value of 177 +/- 10.1 ml to 198 +/- 6 ml and stroke volume significantly (p = 0.01) increased from 120 +/- 6.8 ml to 136 +/- 6.3 ml. Systemic vascular resistance tended to decrease from a mean value of 11.4 +/- 1.28 units to 10.6 +/- 1.10 units. No changes could be observed either in ejection fraction or in cardiac output.(ABSTRACT TRUNCATED AT 250 WORDS)