Enoximone, a new phosphodiesterase-inhibitor with positive inotropic and vasodilating activities is available for intravenous use in patients with severe heart failure. A review of the current knowledge regarding the adverse effects of this substance reveals that they are characterized by cardiovascular, central nervous, and gastrointestinal side effects. Adverse effects occurred in 20% of patients and were mostly due to the pharmacological properties of enoximone. Cardiovascular side effects (10%) were the most frequent; ventricular and supraventricular arrhythmias were most common. Two to three percent of the patients experienced hypotension due to the vasodilator activity of enoximone. Headache, insomnia, and anxiety were the most frequent adverse effects on the central nervous system. Three percent of the patients treated experienced vomiting, nausea, abdominal pain, and diarrhea. An increase of liver enzymes and serum glucose could be observed, mostly in patients with previous liver disease or diabetes. Pharmacokinetic drug interactions are not known; possible pharmacodynamic interactions result from the pharmacological properties of the drugs. Intravenous therapy with enoximone causes a few serious side effects that can only be controlled by careful observation of the patients treated.