Cardiac effects of beta-adrenoceptor blockade with intrinsic sympathomimetic activity during submaximal exercise.

1. beta-adrenoceptor blocking agents with intrinsic sympathomimetic activity (ISA) are characterized by lesser depression of cardiac performance during low levels of sympathetic stimulation than beta-adrenoceptor blocking agents lacking ISA. Studies of the effects of ISA on cardiac output and on the determinants of myocardial oxygen demand during submaximal exercise are described and distinct differences between beta-adrenoceptor antagonists with and without ISA emerge. 2. At doses which produce similar effects on maximal exercise heart rate, and resting and exercise systolic blood pressure, pindolol, a beta-adrenoceptor blocking agent with substantial ISA, allows a higher submaximal exercise cardiac output and submaximal heart rate X systolic blood pressure product than does propranolol, a beta-adrenoceptor antagonist without ISA. 3. These findings may have clinical relevance in specific groups of patients such as those with arterial hypertension, where the preservation of cardiac function may allow for a more physiologic exercise response. Implications in patients with coronary artery disease and chronic heart failure await further study.