BACKGROUND: Recent studies have shown that females have improved myocardial functional recovery, TNFR1 signaling resistance, and increased STAT3 phosphorylation following acute ischemia/reperfusion (I/R) when compared to males. We hypothesized that: 1) STAT3 deficiency in endothelial cells (EC) impairs myocardial functional recovery in both genders, 2) EC STAT3 deficiency equalizes gender differences in functional recovery, and 3) knockout of EC STAT3 decreases activation of myocardial STAT3 and increases p38 MAPK activation following acute I/R. METHODS: Isolated male and female mouse hearts from WT and EC STAT3 knockout (STAT3KO) were subjected to 20 min ischemia/60 min reperfusion, and +/- dP/dT were continuously recorded. Heart tissue was analyzed for the active forms of STAT3 and p38 MAPK, as well as expression of caspase-8 (Western blot) following I/R. RESULTS: EC STATKO had significantly decreased myocardial functional recovery in both genders (% recovered +dP/dt: Male 51.6+/-3.1% vs. 32.1+/-13.1%, Female 79.1+/-3.6% vs. 43.6+/-9.1%; -dP/dt: Male 52.2+/-3.3% vs. 28.9+/-12%, Female 75.2+/-4.1% vs. 38.6+/-10%). In addition, EC STAT3KO neutralized gender differences in myocardial function, which existed in WT mice. Interestingly, EC STAT3 deficiency decreased myocardial STAT3 activation, but increased myocardial p38 MAPK activation, in both genders. However, this was seen to a greater degree in females. CONCLUSION: EC STAT3 deficiency resulted in decreased recovery of myocardial function in both genders and neutralized gender differences in myocardial functional recovery following I/R. This observation was associated with decreased activation of myocardial STAT3 and increased activation of p38 MAPK in EC STAT3KO heart after I/R.