The chemistry, pharmacology, pharmacokinetics, dosage, clinical efficacy, and adverse effects of milrinone are reviewed. Milrinone, which is structurally similar to amrinone, is an oral agent under investigation for the treatment of congestive heart failure. The drug produces positive inotropic and vasodilating effects through unknown mechanisms. Milrinone is well absorbed orally and has a duration of action of three to six hours. The major route of elimination is through the kidneys. The usual initial dosage of milrinone is 2.5-5 mg every six hours; patients whose condition is deteriorating may require 50 mg of the drug per day. Although most patients report that early in therapy the drug relieves the symptoms of congestive heart failure, these benefits are not always sustained. Milrinone does not check the natural progression of disease. Complaints of side effects are rare, although diarrhea, hyperthyroidism, aggravation of angina pectoris, worsening of muscle weakness, and increased fluid retention have been reported. There is evidence to suggest that milrinone may cause or aggravate arrhythmias, worsen congestive heart failure, and shorten the length of survival. Experience with milrinone indicates that the drug may be of limited usefulness in the treatment of congestive heart failure.