The response of thirty-one patients with idiopathic cardiomyopathy to complete prolonged bed rest therapy has been studied. Pertinent clinical features, complications, postmortem findings and other manifestations, including roentgenographic, electrocardiographic and vectorcardiographic changes, are described. Six patients deserted the program. Of the twenty-five who cooperated, four died during initial hospitalization.

Clinical improvement was experienced by all but the four patients who died. In response to prolonged bed rest, of the twentyfive patients who cooperated fully, heart size returned to normal in ten (40 per cent), was partially reduced in nine (36 per cent) and remained unchanged in six (24 per cent).

Early institution of prolonged bed rest after the onset of the signs and symptoms of cardiomyopathy can favorably alter the otherwise poor natural course of the disease. However, relapse is common and often associated with embolic phenomena. In some patients the myocardial disease is irreversible. The studies suggest that the earlier the bed rest is instituted after onset of cardiomyopathy, the greater the benefits to be expected.