Exercise investigations were performed in 39 male hypertensives (WHO stage I-III) to assess haemodynamics and cardiac function after intravenous application of 5 mg propranolol for the detection of latent heart failure. Radiocardiography was used to determine volumetric parameters such as LV end-diastolic volume and ejection fraction, and microcatheterization was employed to obtain the LV filling pressure via pressure measurement in the pulmonary artery (PA). The negative inotropic and chronotropic effects of propranolol on pump function and myocardial mechanics at rest were found to be minimal. During 50 watt exercise however, an increase of the diastolic PA pressure has been observed simultaneously with a diminution of cardiac output (stroke volume being constant). Thus, under acutely administered beta blockade, a general disturbance in the flow-pressure relation could be induced, being comparable to heart failure. Only in a few cases was the reduced contractility compensated by the Frank-Starling mechanism, but only if the mechanism did not participate in the regulation of pump function during the previous control investigation. In other cases a remarkable reduction of cardiac output and even stroke volume occurred, results which may be explained as a consequence of a reduced venous return (or pooling) connected with acutely induced vascular effects (beta-2 blockade).