To evaluate the clinical role of afterload in progression of dilated cardiomyopathy (DCM), a loading examination (study 1) and a follow-up study (study 2) were carried out, using echocardiography, and analysed with Force-Velocity relation (FVR). FVR was defined as the relation between end-systolic wall stress (WSes) and mean circumferential fiber shortening velocity (mVcf). In study 1, the cardiac responses to angiotensin II loading in 30 cases with DCM (17 cases with presumed causes, and 13 without) were observed. These cardiac responses could be described by a hyperbola (Y = 197/(X + 9) + 0.04, r = 0.63) on the graph of FVR, and each response also seemed to fit the hyperbola (Y = a/(X + 9) + 0.04). This "a" value differed according to the presumed causes, and had an inverse correlation with % fibrosis in the biopsied cardiac muscle (Y = 0.86 + 29.9, r = -0.64, p less than 0.02). In study 2, during a mean clinical course of 3.7 years, the cardiac function (mVcf) in 19 out of 25 cases with DCM changed inversely with the changes of WSes on FVR. The "a" value calculated by the same method as study 1 did not differ before and after the follow-up. It did, however, vary according to the clinical outcome. These results suggest that afterload plays an important role in progression of DCM, and that an evaluation of cardiac function employing FVR may be helpful for assessing the myocardial damage, causative factors, and the prognosis of DCM.