The effects of hemodialysis on cardiac performance were evaluated by systolic time intervals measured blindly in 15 chronic renal failure patients maintained free of circulatory congestion. After a mean dialysis of 8.7 hours, levels of blood urea nitrogen, serum creatinine, and potassium and body weight showed statistically significant decreases and serum calcium and hematocrit values increased; heart rate and both diastolic and systolic blood pressure did not change significantly. Left ventricular ejection time (LVET) and ejection time index (ETI) were significantly shorter, falling from within normal limits to below normal. Pre-ejection period (PEP) rose significantly. These changes are consistent with a two-fold immediate effect of hemodialysis: (1) reduction of stroke volume as reflected by decreased ETI; and (2) reduced Starling effect, with or without decreased contractility, as reflected by increased PEP.