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Milrinone is a noncatecholamine, nonglycoside drug that has both positive inotropic and vasodilator properties. That is, milrinone increases the force of cardiac contraction and decreases the constriction of blood vessels. It acts by blocking a key enzyme (cAMP-specific cardiac phosphodiesterase F III) responsible for reducing the effects of norepinephrine. (Norepinephrine constricts vascular smooth muscle.) Milrinone has been shown to be an effective drug in the treatment of severe heart failure, a disease characterized by ineffective cardiac contraction and insufficient cardiac output. It has not been evaluated in the treatment of individuals recovering from cardiac surgery, another group of patients who suffer from insufficient cardiac output. To determine whether milrinone is beneficial for such patients, its effects were evaluated in 99 otherwise healthy patients undergoing elective cardiac surgery (coronary artery bypass grafting, atrial and mitral valve replacement). Following surgery, patients were intravenously administered one of three doses of milrinone for a minimum of 12 hours. In all cases, drug administration was associated with a rapid, sustained improvement in cardiac output, and a decrease in vascular resistance (reflecting vascular relaxation). Increases in heart rate also occurred. Possible adverse side effects (nausea and cardiac arrhythmias) were noted in about half the patients, but these symptoms are common in patients recovering from heart surgery, and could not be unequivocally associated with drug treatment. (Consumer Summary produced by Reliance Medical Information, Inc.)