Optimal cardiac output (CO) resuscitation for severely burned guinea pigs is obtained with intravenous volumes of lactated Ringer's (LR) calculated at 4 cc/kg/%burn/24 hr. When one half this volume of LR is given (2 cc/kg/%burn/24 hr) CO is significantly (p < 0.05) reduced at 2, 4, and 8 hours after injury. When early postburn cimetidine therapy (0.5 hours after injury) is added to only 1 cc/kg/%burn/24 hr LR, CO is significantly elevated for the same time periods and is not significantly different from CO values of LR at 4 cc/kg/%burn/24 hr for the first 24 hours after injury. However, postburn cimetidine therapy delayed until 1 hour after burn injury did not improve CO compared to treatment with LR at 2 cc/kg/%burn/24 hr. These observations suggest that early postburn cimetidine therapy administered within 1/2-hour of severe scald injury will result in significant CO improvement while simultaneously reducing resuscitative fluid volume requirements by as much as 70% for the first 24 hours after injury.