Nonselective beta-receptor stimulation and blockade and left ventricular function.

The effects of increasing doses of intravenous isoproterenol on left ventricular (LV) size and function were assessed before and after oral propranolol (80 mg). Eleven normal subjects were studied by M-mode echocardiography. The isoproterenol dose was increased until heart rate had risen by 25 to 30 b.p.m. LV end-diastolic (LVED) dimension (46.6 +/- 1.3 mm) was increased by isoproterenol (to 48.8 +/- 1.5 mm) and decreased by propranolol (to 45 +/- 1 mm). LV end-systolic dimension was decreased by isoproterenol and increased by propranolol. Isoproterenol increased LVED dimension despite the opposing effect of the tachycardia, whereas propranolol decreased LVED dimension despite its negative inotropic and chronotropic effects. These results suggest that nonselective beta-receptor stimulation or blockade can affect cardiac output through direct cardiac actions and by influencing venous return.