Clinical relevance of intrinsic sympathomimetic activity of beta blockers.

beta-Blockers are effective in the symptomatic relief of angina pectoris by decreasing myocardial oxygen demand during effort and emotional stress. Agents with ISA such as pindolol produce effective beta-blockade during effort or emotional stress while conferring significant protection from myocardial depression and bradycardia at rest. In addition, agents with ISA have been shown to depress respiratory function to a lesser extent and to induce fewer peripheral vascular side effects than compounds devoid of this property. These potential effects of ISA may be counterbalanced by the consideration that ISA may be undesirable in angina occurring at rest or at low exercise levels. Additional well-controlled trials in patients with angina and resting bradycardia or impaired left ventricular function are needed to further document the clinical importance of ISA.