We studied the effects of dopexamine hydrochloride in 14 patients following cardiopulmonary bypass for coronary revascularisation (12 patients) or valve replacement (2 patients). The drug was administered by intravenous infusion at rates of 1, 2, 4 and 6 micrograms/kilogram/minute for a period of 10 minutes at each dose. Measurements of heart rate, blood pressure, right atrial pressure, pulmonary arterial pressure, pulmonary arterial wedge pressure and cardiac output (thermodilution method) were made at the end of each period. There were significant increases in heart rate (P less than 0.05), cardiac index (P less than 0.05) and systolic blood pressure (P less than 0.05). There were significant falls in systemic vascular resistance (P less than 0.05) and pulmonary vascular resistance (P less than 0.05). There were no significant changes in pulmonary arterial or wedge pressure. No serious adverse effects were observed. Dopexamine hydrochloride appears to be a useful supportive agent in patients following cardiopulmonary bypass, although further trials need to be carried out in order to establish precise therapeutic indications for its use.