Preconditioning (PC) protects against ischemia/reperfusion injury via activation of the JAK-STAT pathway. We hypothesized that the mediators responsible for preconditioning can be transferred to naive myocardium through the coronary effluent. Langendorff perfused hearts from male Sprague-Dawley rats were randomized to paired donor/acceptor protocols with or without preconditioning in the presence or absence of the JAK 2 inhibitor AG490 (n=6 for each group). Warmed, oxygenated coronary effluent collected during the reperfusion phases of preconditioning (3 cycles, 5 minutes ischemia/5 minutes reperfusion) was administered to acceptor hearts. Hearts were then subjected to 30 minutes ischemia/40 minutes reperfusion (I/R). Left ventricles were analyzed for pSTAT-1, pSTAT-3, Bax, Bcl, Bad and Caspase-3 expression by western immunoblotting. A separate group of hearts (n=6) were analyzed for STAT activation immediately after transfer of PC effluent (no I/R). Baseline cardiodynamics were not different amongst the groups. End-reperfusion +dP/dtmax was significantly (P<0.05) improved in acceptor PC (3637±199 mmHg/s) hearts and donor PC hearts (4304±347 mmHg/s) over non-preconditioned donor (2020±363 mmHg/s) and acceptor hearts (2624±345 mmHg/s). Similar differences were seen for &#61485;dP/dtmin. STAT-3 activation was significantly increased in donor and acceptor PC hearts compared to non-PC hearts. Conversely, pSTAT-1 and Bax expression was decreased in donor and acceptor PC hearts compared to non-PC hearts. No differences in Bcl, Bad or Caspase-3 expression were observed. Treatment with AG490 attenuated recovery of ±dP/dt in acceptor PC hearts and significantly reduced pSTAT-3 expression. Preconditioned coronary effluent activates JAK-STAT signaling, limits apoptosis and protects myocardial performance from ischemia/reperfusion injury.