The treadmill exercise test with the Bruce protocol was performed in three patients with post-myocarditic myocardial hypertrophy (PMH) and ten patients with cardiomyopathy, including three with dilated cardiomyopathy (DCM), five with hypertrophic obstructive cardiomyopathy (HOCM), and two with hypertrophic and nonobstructive cardiomyopathy (HCM). The endurance time was below the normal level in all but one case and was normal or near normal in the three cases with PMH. ST depression was observed in five cases, none of which were of HCM. A marked increase in amplitude of the negative phase of the P wave in V1 was observed in one patient with DCM. The response of blood pressure during the exercise was abnormal in patients with DCM and HCM but was normal in PMH.