Abstract Twenty-one patients with a diagnosis of idiopathic cardiomyopathy were studied clinically and hemodynamically. Catheterization of the right and left heart chambers with selective cineangiographic studies from the left ventricle and the aortic root are presented. The patients exhibited different patterns of failure that reflected more than one mode of adaptation of the circulation to left ventricular failure. All 12 patients in whom cineangiograms were performed demonstrated an increased transverse diameter of the left ventricle in end-systole and end-diastole. Three of these patients had normal pressures and flows at rest and on exercise. One of the 3 had never been clinically in failure, suggesting that ventricular dilatation as an isolated abnormality may precede the onset of other hemodynamic and clinical changes. An adequate appraisal of the hemodynamics should encompass ventricular volumes as well as filling pressures and flows.