Arachidonic acid (AA) metabolism by infarcted canine myocardium was studied and correlated with matched histologic analyses following permanently occluded or reperfused infarction. Histologic analysis of tissues from reperfused infarcts showed a marked acceleration of inflammatory cell invasion and of granulation tissue formation when compared to the occlusive infarct. In the reperfused infarct, polymorphonuclear leukocytes (PMNs) were very prominent at one day after infarction while in the occlusive infarcts the neutrophilic invasion was less intense but more sustained. At one day following reperfused infarction the major arachidonate product, which co-migrated by thin layer chromatography with the mono-hydroxyeicosatetraenoic acids (HETEs), was significantly elevated (254 ± 49 pmoles/gm wet weight, n=3) when compared to normal tissue (48 ± 6 pmoles/gm n=19). This occured at a time when the number of PMNs was maximal in the infarcted tissue. Addition of the calcium ionophore A23187 caused a further marked stimulation in HETE production in the one day reperfused infarct but not at the other time points studied. The production of HETE was not significantly different in the infarcted tissue than in the normal tissue at three and seven days following reperfused infarction or at one, three, or seven days after occlusive infarction. The identity of this HETE product was investigated using reverse phase high performance liquid chromatography (RP-HPLC) and gas chromatography-mass spectrometry (GC-MS) and found to be predominantly 12 - hydroxy - 5,8,10,14 - eicosatetraenoic acid (12-HETE) with a small amount of 15-HETE. Thus the production of 12-HETE parallels the number of neutrophils invading the infarcted area of the heart.