Until recently, patients with aortic insufficiency and congestive heart failure have been offered only the temporary palliation provided by rest, diet, cardiac glycosides, and diuretics. A more direct therapeutic approach would aim at correction of the basic hemodynamic defect, by mechanical reduction of the volume of regurgitation. Hufnagel (1) has devised a surgical procedure for altering the abnormal pattern of blood flow in aortic insufficiency. A plastic ball valve is inserted in the thoracic aorta, immediately distal to the left subclavian artery. This prosthesis prevents regurgitation of the blood traversing it, estimated to be approximately 75 per cent of the total cardiac output (2) (Figure 1). Blood flow above the valve, in the coronary, carotid, and subclavian systems remains regurgitant. To date, over twenty-five patients have been treated successfully in this manner (3, 4). Clinical observations suggest that patients with severe aortic insufficiency and varying degrees of cardiac decompensation benefit markedly by this operation, showing postoperatively increased exercise tolerance and clearing of the signs of heart failure. The present study was undertaken in order to demonstrate objectively the alterations in circulatory dynamics produced by the valvular prosthesis.