Enoximone is an imidazolone derivative currently undergoing trials in patients with congestive heart failure refractory to conventional therapy. It is a phosphodiesterase inhibitor with both positive inotropic and vasodilator properties, and is active by both oral and intravenous routes of administration. While pharmacodynamic studies have documented beneficial haemodynamic effects after short term oral administration, and objective and subjective improvement relative to placebo during some short term trials, its clinical efficacy during continuous longer term therapy remains uncertain. Enoximone is of potential benefit as an adjunct in short term management of patients with end-stage cardiac failure awaiting cardiac transplantation. In the usually small studies reported to date enoximone was generally better tolerated at oral dosages of less than 2 mg/kg than at higher dosages. Thus, while its pharmacodynamic profile holds potential promise in a difficult therapeutic area, the long term clinical efficacy and tolerability of enoximone remain yet to be determined in controlled trials of adequate size and duration.