The metabolites of prostacyclin (PGI2) and thromboxane A2 (TxA2), 6-keto-PGFια and thromboxane B2 (TXB2), were investigated during reperfusion (RP) following warm (37 °C, 60 min, n = 9) or cold (15 °C, 120 min, n = 11) ischemia induced by cold (4 ° C) or normothermic (30 °C) K+ cardioplegia (CP) in isolated canine hearts subjected to global ischemia and RP. 6-Keto-PGF1α flux was significantly higher (p < 0.025) in the warm group at 1, 5, and 10 min of RP (4,202 ± 1,412, 2,475 ± 1,875, and 1,255 ± 633 pg/g·min, mean ± SD) compared to those in the cold group (1,504 ± 1,245, 434 ± 641, and 370 ± 329 pg/g·min). TxB2 flux was small in amount compared to 6-keto-PGF1α in both groups. Regarding the coronary hemodynamics, the cold group alone showed statistically significant relationships of coronary sinus blood flow to TxB2 level and TxB2/6-keto-PGF1α ratio in coronary sinus blood. Also, coronary vascular resistance showed linear relations to these two parameters of the metabolites. In a supplementary experiment only with cold ischemia for 180 min, 6-keto-PGF1α was released at each coronary flush-out by CP and the incremental amount showed a gradual increase during ischemia. These results indicated that significant production and release of PGI2 occurred during ischemia and RP following CP arrest and these related to the degree of myocardial damage while the response of TxA2 seemed less significant. The role of PGI2 release during RP following cardioplegic ar