The extent and time course of recovery of left ventricular function were investigated in 29 patients with no previous symptoms who had acute nonischemic congestive cardiomyopathy and left ventricular ejection fraction of 0.22 +/- 0.07. Improvement in left ventricular ejection fraction by at least 0.05 was observed in 24 of the 29 patients and was achieved within 6 months after the initial evaluation. Progressive improvement was seen, with a maximum ejection fraction of 0.45 +/- 0.17 being achieved within approximately 18 months. The degree of ejection fraction recovery was not related to the initial clinical or hemodynamic variables. However, the extent of fibrosis detected on endomyocardial biopsy correlated inversely with subsequent changes in ejection fraction (r = -0.65, p = 0.0003). Thus significant recovery is likely after an acute episode of nonischemic cardiomyopathy and may be progressive during the first year. Recovery is related to the extent of myocardial fibrosis detected on endomyocardial biopsy but cannot be predicted from the initial clinical or hemodynamic presentation.