The haemodynamic effects of high or low doses of furosemide used to prevent overt left heart failure (LHF) in acute myocardial infarction (AMI) were studied. Fifteen consecutive AMI patients without overt LHF and with a cardiac index (CI) of 2.6 +/- 0.5 l min-1 m-2, a right atrial mean pressure (RAMP) of 7 +/- 3 mmHg and a pulmonary arterial diastolic pressure (PADP) of 14 +/- 4 mmHg were investigated during 24 h. A high dose group (HDG) received 40 mg furosemide t.i.d. and a low dose group (LDG) 20 mg once daily. Following the first 40 mg of furosemide (HDG), the stroke volume index (SVI), CI, RAMP and PADP decreased. The heart rate and systemic vascular resistance index (SVRI) increased. Following the first 20 mg of furosemide (LDG), the only significant change was a decrease in PADP. After 24 h, the heart rate in the HDG was further increased; the SVI, RAMP and PADP were further reduced, whereas CI was similar to that before. In the LDG, the heart rate, SVI and CI remained unchanged. All pressures tended to decline and the SVRI was lower than in the HDG. Thus, repeated injections of 40 mg of furosemide induced a sustained preload reduction in AMI patients without overt LHF, but this was associated with potentially disadvantageous haemodynamic findings.