Left ventricular (LV) function was quantitated in 14 patients with peripartum cardiomyopathy, in 10 using 2-dimensional (2-D) echocardiography and in 4 radionuclide ventriculography, and values were compared with those in 11 normal women in the immediate postpartum period. LV end-diastolic and end-systolic volume indexes, LV wall mass index and ejection fraction were calculated during the acute phase of the illness and serially through long-term follow-up (mean 24 months). During the acute phase of illness there was marked LV dilatation: mean end-diastolic volume index was 95 +/- 22 ml/m2, vs 67 +/- 9 ml/m2 in control subjects (p less than 0.005), and mean end-systolic volume index was 66 +/- 18 ml/m2, compared to 27 +/- 5 ml/m2 in control subjects (p less than 0.001). Mean heart rates and mean systolic pressures in the patients with peripartum cardiomyopathy and the control subjects were similar, 91 +/- 24 vs 79 +/- 14 beats/min and 120 +/- 14 vs 117 +/- 10 mm Hg, respectively. LV wall mass index was higher, 139 +/- 38 vs 96 +/- 8 g/m2 (p less than 0.005), and ejection fraction much lower, 29 +/- 5% vs 67 +/- 5% (p less than 0.001), in control subjects. Five patients underwent endomyocardial biopsy during the acute illness, which showed interstitial fibrosis but no evidence of active inflammation. There was rapid and early improvement in LV function in 13 of 14 patients. Changes in LV volume, mass and ejection fraction all followed an exponential time course during LV remodeling.(ABSTRACT TRUNCATED AT 250 WORDS)