The hypothesis that mild decreases in myocardial function may occur with preservation of normal levels of intramyocardial ATP was tested. A model of single vessel coronary stenosis using eight mongrel dogs in an open chest preparation was used. Myocardial oxygen supply was altered by performing acute normovolemic hemodilution with a colloid solution. The results demonstrated significant alterations in myocardial ATP content with hemodilution-induced mild regional dysfunction, which was not in line with the hypothesized effects of ischemia on myocardial function. In addition, restoring myocardial function by minimal reinfusion of shed blood in this study did not restore myocardial energy stores, an effect that may be called metabolic stunning. The results suggest that myocardial stunning may not be an important and ubiquitous process during intraoperative myocardial ischemia. Further, myocardial function appears to be capable of quickly recovering from mild ischemia although metabolic function may be slower. Finally, the concept of decrements in myocardial function occurring in order to preserve myocardial metabolic stores does not appear to occur universally, which may be significant in the prevention or treatment of mild perioperative ischemia.