Five days were allowed between successive drug administrations and the order of drug administration was randomized. Heart rate, arterial pressure, oxygen consumption, minute ventilation and CO2 production were monitored. Plasma drug concentrations were measured at the time of exercise. Judged'by plasma levels, propranolol was about three times more potent than metoprolol in attenuating heart rate. Both drugs produced a wide variation in plasma levels after a given oral dose, and both'drugs attenuated the systolic blood pressure response to exercise. Neither drug affected diastolic blood pressure or maximum oxygen consumption, maximum minute ventilation or the anae'robic threshold. We conclude that there is no evidence that the cardioselective drug metoprolol is superior to propranolol in terms of the ability to perform or respond to short-term maximal exercise. In addition, the fact that maximal oxygen consumption and the anaerobic threshold were unaffected implies that fatigue during exercise while on g-adrenergic blocking drugs is'not due to an effect of these drugs in limiting blood flow to the exercising extremities.THE f3-ADRENERGIC blocking drugs propranolol and metoprolol are used widely in the treatment of patients with hypertension, ischemic heart disease and a variety of other conditions. Metoprolol is cardioFrom the Divisions of Cardiology and Clinical Pharmacology,

In detecting documented coronary artery disease, the sensitivity of arbutamine testing was equal to that of exercise for the electrocardiographic end point of ST segment change alone. Arbutamine testing was significantly superior to exercise testing for either ST change or angina or for angina alone.

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