Eight patients with chronic renal failure, who were on chronic hemodialysis were studied. The systolic time intervals were measured from simultaneous recordings of the electrocardiogram, phonocardiogram and carotid arterial pulse tracing. The ventricular volumes and stroke volume were calculated from echocardiographic recordings. The following indices of contractility were derived from the echocardiographic traces - the mean circumferential fiber shortening rate (mean VCF), and mean posterior wall velocity (PWV), mean normalized posterior wall velocity (VPW), and mean normalized interventricular septal velocity (VIVS). The studies were performed immediately before and after a routine dialysis. All the patients had abnormal end diastolic volumes in the basal state. After dialysis the end diastolic volume, stroke volume and left ventricular ejection time were reduced significantly. These changes in cardiac pump function reflect the post dialysis reduction of blood volume. The values for the contractility indices all improved after dialysis and this change correlates well with the abbreviation of left ventricular ejection time (r = .92). It is concluded that the main effects of dialysis are on pump function, and although the changes in the normalized velocities may indicate a real improvement in contractility, their validity is limited by their dependence on left ventricular load conditions and ejection time. Echocardiographic determination of ejection fraction and mitral valve E point - septal separation are suggested as reliable indices of cardiac pump function.