Survival after myocardial infarction decreases with left ventricular dilatation, although dilatation at 4 weeks was found to be compensatory. To study this apparent discrepancy, prospective simultaneous volume and hemodynamic measurements at rest were extended in 39 patients with small and 37 with large myocardial infarctions from 4 days (range, 2-6 days) and 4 weeks (range, 3-5 weeks) to 6 months (range, 5-8 months) after infarction and were repeated during supine bicycle exercise at 50 W. In patients with small infarction, end-diastolic volume (mL/m2) decreased from 4 days to 6 months; ejection fraction (%), stroke volume (mL/m2), and end-systolic volume (mL/m2) remained unchanged. Stroke index rose during exercise at 4 weeks and 6 months. In patients after large infarction (n = 37), left ventricular end-systolic volume index (4 days, 38 +/- 3; 4 weeks, 47 +/- 3*; 6 months, 52 +/- 3*; *p < 0.05 versus 4 days) and end-diastolic volume indexes (4 days, 72 +/- 3; 4 weeks, 86 +/- 5*; 6 months, 92 +/- 5*; *p < 0.05 versus 4 days, +p < 0.05 versus 4 weeks) increased at constant wedge pressure. Stroke index remained restored beyond 4 weeks after infarction (4 days, 35 +/- 2; 4 weeks, 42 +/- 2*; 6 months, 42 +/- 2*; p < 0.05 versus 4 days) and rose during exercise at 4 weeks (rest, 45 +/- 2; exercise, 55 +/- 3; p < 0.05) but not at 6 months (rest, 42 +/- 3; exercise, 45 +/- 3; p = NS).(ABSTRACT TRUNCATED AT 250 WORDS)