1. Intravenous frusemide has been given to thirty-five patients with myocardial infarction and clinical signs of left ventricular failure. The haemodynamic changes following frusemide were then observed over the subsequent 6 h.
2. Frusemide produced a large diuresis, which was maximal during the first 2 h but fluid depletion was maintained at 24 h. The greatest diuresis occurred in patients with the highest stroke index.
3. All patients showed a fall in pulmonary artery pressure after frusemide. In patients with evidence of poor left ventricular function (low stroke index, high pulmonary artery pressure) this was associated with little change in stroke index. In patients with less severe impairment of left ventricular function there was an initial fall in stroke index at 1 and 2 h.
4. Six hours after frusemide there was a reduction in both pulmonary artery pressure and systemic arterial pressure; the latter correlated with the volume of the diuresis.