The haemodynamic and biological effects of intravenous milrinone were studied in 24 adult patients with a low cardiac output syndrome following cardiac surgery. The patients received a milrinone bolus of 50 micrograms kg-1 over 10 min followed by a 0.375-0.750 micrograms kg-1 min-1 infusion over 48 h. After the first hour of treatment, an increase in cardiac index, systolic index and left ventricular stroke work index, and a decrease in right and left loading pressures, pulmonary artery pressure, systemic vascular resistance and pulmonary vascular resistance were observed while heart rate and systemic arterial pressure were not modified. These haemodynamic effects were maintained over the 48 h of treatment and persisted 3 h after discontinuation of treatment. Milrinone, which possesses inotropic and vasodilatory effects, increased cardiac performance and corrected the low cardiac output in all patients.