Preload and afterload were controlled intraoperatively in 2 groups of patients with valvular regurgitation and congestive heart failure in order to determine the effect of fluid loading on weight gain and subsequent recovery. As a part of their anesthetic management before cardiopulmonary bypass, 16 patients were given 1 liter of crystalloid with nitroprusside infused at 1 microgram/kg/min and 16 received 4 liters of crystalloid with nitroprusside at 4 micrograms/kg/min. Arterial and filling pressures were kept the same in both groups. Heart rate and vascular resistance became significantly lower and cardiac index and stroke volume significantly higher in the fluid-augmented group. The transition to cardiopulmonary bypass was smoother for the fluid-augmented patients. All patients survived, and 2 in each group were ventilated beyond 24 hours. The mean weight gain at surgery was the same in the 2 groups (3 kg). For the first 2 postoperative days, body weight remained unchanged and thereafter, both groups lost weight at 0.6 kg/day. Preoperative weight was reached on day 7 and discharge occurred on day 15, 2 kg below control. Thus, a modest operative weight gain in these patients is inevitable, benign, and independent of the volume of fluid infused before bypass.