intrinsic sympathomimetic effect

ISA is the abbreviation for intrinsic sympathomimetic activity of some beta blockers. These beta blockers show partial beta-adrenergic agonist responses side-by-side with receptor antagonistic responses. The clinical effect depends largely on the underlying sympathetic tone in the patient: A low tone would result in a restraining effect (with lowering the heart rate), whereas a high tone would leave the heart rate uneffected or increase it slightly.