Effect of beta adrenergic blockade on left ventricular function in exercise

The effect of beta adrenergic blockade with propranolol on left ventricular diameter during exercise was investigated in dogs running on a treadmill. Cardiac output was substantially reduced by propranolol at all levels of exercise. Stroke volume was reduced by 22, 27, and 23% for mild, moderate, and severe exercise, respectively, due to elevations in left ventricular end systolic dimensions. During mild and moderate exercise, the Frank Starling mechanism compensated partially for the loss of the sympathetic inotropic and chronotropic effects. However, during severe exercise there were no significant differences between intact and beta blocked exercise in end diastolic left ventricular diameter.