Although the prognosis of dilated cardiomyopathy (DCM) is poor, some patients occasionally follow favorable clinical courses and have significant improvement in cardiac function. To elucidate the mechanism of such improvement, we compared the clinical and pathological findings of 54 cases with DCM, including 12 cases with significant improvement (Dd less than 55 mm, %FS greater than 22%) during two years' follow-up (improved group), 26 without significant improvement (unimproved group), and 16 who died within two years (decreased group). Percent fractional shortening (%FS) in the deceased group was less than that in the unimproved group (12.4 +/- 3.9 vs 17.2 +/- 6.2, p less than 0.01). Pulmonary capillary pressure (PC) and % fibrosis in the deceased group were greater than those in the unimproved group [(22.7 +/- 9.5 vs 11.4 +/- 4.2 mmHg, p less than 0.001), (21.7 +/- 9.9 vs 13.4 +/- 3.6, p less than 0.01)], respectively. Although Dd, Ds, %FS, end-diastolic wall thickness (Thd), and PC in the improved group were not different from those in the unimproved group. End-systolic wall stress (WSes) in the improved group was greater than that in the unimproved group (376 +/- 73 vs 319 +/- 60 g/cm2, p less than 0.02), but % fibrosis was less in the improved group (7.6 +/- 3.4 vs 13.4 +/- 3.6, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)