Left ventricular angiography and endomyocardial biopsy were performed in 10 patients with aortic insufficiency and in 10 patients with congestive cardiomyopathy. Muscle fibre diameter and interstitial fibrosis were determined. In aortic insufficiency the diameter of muscle fibres is highest in the endstage, while in congestive cardiomyopathy it is highest in the earliest stage.