There is no evidence regarding the effect of stunning on maximization of regional myocardial external work (EW) or efficiency of energy transfer (EET) in relation to regional afterload (end-systolic stress, sigma(es)). To that end, we studied these relationships in both the left anterior descending coronary artery (LADCA) and left circumflex coronary artery regions in anesthetized, open-chest pigs before and after LADCA stunning. In normal myocardium, EET vs. sigma(es) was maximal at 75.4 (69.7-81.0)%, whereas EW vs. sigma(es) was submaximal at 12.0 (6.61-17.3) x 10(2) J/m(3). Increasing sigma(es) increased EW by 18 (10-27)%. Regional myocardial stunning decreased EET (27%) and EW (36%) and caused the myocardium to operate both at maximal EW (EW(max)) and at maximal EET (EET(max)). EET and EW became also more sensitive to changes in sigma(es). In the nonstunned region the situation remained unchanged. Combining the data from before and after stunning, both EW(max) and EET(max) displayed a positive relationship with contractility. In conclusion, the normal regional myocardium operated at maximal EET rather than at maximal EW. Therefore, additional EW could be recruited by increasing regional afterload. After myocardial stunning, the myocardium operated at both maximal EW and maximal EET, at the cost of increased afterload sensitivity. Contractility was a major determinant of this shift.