In 14 patients with chronic renal failure and without obvious signs of congestive heart failure, cardiac function was analyzed immediately before and after hemodialysis through radiocardiography, phonocardiography and X-ray examination. Plasma creatinine, urea nitrogen and body weight were reduced by hemodialysis, whereas electrolyte levels remained relatively constant. Cardiac output, stroke volume, arterial pressures, and left ventricular work were generally elevated in these patients before hemodialysis, and were not affected by the procedure. Changes in heart volume, mean ejection rate, Lüthy’s index, and gallop sounds suggested an improvement of heart function after hemodialysis. In the absence of typical heart failure, an excessive water load may deteriorate cardiac performance in these patients by cardiac enlargement concomitant with hypertension. Thus overhydration should be avoided and cardiac function assessed by radiologic measurement of heart size and phonocardiography.