Abstract The hemodynamic effects of intra-aortic balloon augmentation (IABA) in the proximal descending aorta were determined in 18 intact, anesthetized dogs. Helium was the inflating gas and deflation was vacuum assisted. Myocardial depression and shock were induced by intravenous propranolol (1 to 2 mg. per kilogram) and a continuous procainamide (0.2 to 1 mg. per kilogram per minute) infusion. Hemodynamic measurements were determined before and during drug shock and 15 to 60 minutes after IABA. During IABA, cardiac output rose 35 percent in 14 of 17 dogs secondary to increased stroke volume. Mean arterial pressure rose 41 percent during IABA in 14 of 17 dogs and persisted after IABA was discontinued. Systemic end diastolic pressure decreased in all dogs. Carotid artery dp dt rose to near control levels following IABA, mainly as the result of decreased systolic outflow impedance. The length of the pre-ejection period was decreased by only ten percent; this did not indicate any measurable improvement in myocardial contractility. Peripheral vascular resistance was variably changed. IABA appears to improve many adverse hemodynamic changes of drug-induced myocardial depression and shock.