Ventricular performance was assessed before and after angiocardiography in 22 patients with normal left ventricle, mitral stenosis, aortic stenosis, and myocardial disease. The increased circulating blood volume known to occur after angiocardiography is a determinant of the increased ventricular pre-load. The after-load is unchanged. Patients with normal left ventricle and some patients with valve stenosis responded by an increase in the work performed and some had only a minimal or no increase. A group of patients with serious heart disease performed less work. If the ventricular response can be considered on the basis of the Frank-Starling principle, then the abnormal response of such patients is due to an altered length-tension relationship.