In severe chronic congestive cardiac failure the physician has the choice of two families of positive inotropic agents, the direct sympathomimetics and the phosphodiesterase inhibitors. The aim of the study was to compare the efficacy and tolerance of enoximone and dobutamine in this indication. Twenty patients with severe chronic cardiac failure with a cardiac index of less than 2.2 l/min/m2 and pulmonary capillary pressure of over 20 mmHg were randomised into two groups in an open trial. One group received enoximone 50 micrograms/kg/min for 30 minutes then 10 micrograms/kg/min and the other received dobutamine 10 micrograms/kg/min. The two groups were comparable. Results were analysed 12 hours after starting therapy, well after the loading dose of enoximone and before the appearance of tolerance to dobutamine. Neither drug caused a significant change in heart rate or mean blood pressure. The pressure-rate product did not increase significantly with enoximone (+9.2% NS) in contrast with the dobutamine group in which a significant elevation was observed (+23.5%, p less than 0.05). The cardiac index increased with enoximone (+61.0%, p less than 0.01) and with dobutamine (+32.1%, p less than 0.02). This resulted mainly from an increase in the systolic index (+45.5%, p less than 0.05 with enoximone and +30.1%, p less than 0.05 with dobutamine). Pulmonary capillary pressure and total systemic resistance decreased with enoximone (-29.1%, p less than 0.001 and -36.7%, p less than 0.05 respectively) and with dobutamine (-23.4%, p less than 0.001 and -20.7%, p less than 0.05 respectively).(ABSTRACT TRUNCATED AT 250 WORDS)