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The coronary arteries supply blood to the heart, and when they become occluded or narrowed, the diminished blood supply to the heart (myocardial ischemia) can cause pain (angina), heart damage, and sometimes death. In the condition known as unstable angina, myocardial ischemia has progressed to the point where worsening chest pain sometimes signals an impending myocardial infarction (heart attack). A class of drugs known as beta-adrenergic blocking agents, or beta blockers, has been shown to be useful in the treatment of myocardial ischemia. However, in patients with unstable angina, administration of long-lasting beta blockers can sometimes lead to adverse side effects. The development of the ultra short-acting cardioselective beta blocker esmolol has provided a drug that can be administered by continuous intravenous infusion, allowing a minute-by-minute titration of the dose level. To provide data on the use of esmolol in patients with acute myocardial ischemia, 21 patients who had persistent angina despite conventional medical therapy were given this drug. The dose was adjusted on an individual basis to provide a predetermined alteration in cardiovascular function (20 percent decrease in the rate-pressure product). Esmolol administration was effective in alleviating chest pain in 18 of the 21 subjects (86 percent). Seven patients eventually underwent percutaneous transluminal coronary angioplasty (reopening the narrowed segments of the coronary arteries with an inflatable balloon-tipped catheter), eight underwent coronary bypass surgery, and the remainder were discharged and received drug therapy, which included beta blockers. Other than a transient hypotension (excessively low blood pressure), which was corrected with decreased drug dose, there were no significant side effects related to esmolol administration. (Consumer Summary produced by Reliance Medical Information, Inc.)