A double-blind, randomized, concurrent trial of enoximone vs placebo was undertaken to assess the efficacy and safety of enoximone, 100 mg t.d.s. added to optimal therapy in 30 patients (mean age, 66.4 +/- 14 years) with severe congestive heart failure. Before inclusion, all patients remained markedly symptomatic despite treatment with diuretics, digitalis, vasodilators and angiotensin converting enzyme inhibitors. Symptoms and quality of life were evaluated at inclusion, and at days 4 and 31; 24-hour electrocardiography and Doppler echocardiography were performed at inclusion and at day 31. Clinical and echocardiographic baseline characteristics were similar in the two groups. During the study, 10 patients dropped out: 3 in the enoximone group (1 death) and 7 in the placebo group (3 deaths). At day 4, symptoms were improved in 13 enoximone-treated patients and in 8 patients on placebo (P less than 0.05). At day 31, symptoms were still improving in 10 of 12 patients on enoximone and in 6 of 8 patients on placebo (NS). No serious clinical side-effects were reported, and no statistically significant difference in the frequency of premature ventricular contractions between the two groups was apparent on Holter monitoring. Peak acceleration of ascending aortic blood flow at entry was 17 +/- 6 m/second2 in the enoximone group and 18 +/- 5 m/second2 in the placebo group (NS). At day 31, the change in peak acceleration was +20% in the enoximone group vs -6% in the placebo group (P less than 0.05). Cardiac index increased by 18% in the enoximone group (from 2.17 +/- 0.7 litres/minute/m2 to 2.4 +/- 1.0 litres/minute/m2 (NS).(ABSTRACT TRUNCATED AT 250 WORDS)