17 patients with New York Heart Association (NYHA) class IV congestive cardiac failure, refractory to conventional treatment, were additionally treated with oral metolazone (1.25-10 mg daily). 12 improved sufficiently to be discharged from hospital (NYHA class II or III, mean weight loss 8.3 kg), 1 of whom died at home 4 weeks later. The other 5 patients were treated with intravenous dobutamine for 72 h; 2 responded (average weight loss 4.4 kg), and 2 responded to subsequent reintroduction of metolazone. 4 of these 5 patients died, 2 in hospital of acute myocardial infarction. Overall, 15 patients with very severe refractory cardiac failure improved sufficiently to be discharged from hospital. Treatment was associated with mild transient hypokalaemia in 7 patients, and hyponatraemia and renal impairment in 1, for whom metolazone dosage had to be reduced. Failure to respond to the introduction of metolazone may indicate an especially poor prognosis.