Infarcted porcine heart tissue and surrounding tissue were investigated for the content of plasmalogens and oxidatively derived corresponding alpha-hydroxyaldehydes as well as for products of lipid peroxidation, e.g. malondialdehyde, glyoxal, 2-hydroxyheptanal and oxygenated fatty acids. Oxidation products of unsaturated fatty acids and plasmalogens were accumulated in infarcted tissue compared to the surrounding one. Their amounts increased with time of ischemia. In addition leukotoxins (9, 10-epoxy-12-octadecenoic acid and 12,13-epoxy-9-octadecenoic acid) as well as other epoxides of unsaturated fatty acids were identified. These compounds are absent in healthy heart tissue. Some of the monohydroxy fatty acids, found in comparable high yield, can not be derived from LPO processes. They are obviously generated from epoxides. Their distribution pattern indicates that they originate by an enzymic rather than by an autocatalytic process. We assume that the enzymes are activated by cell injury due to infarction. Linoleic acid seems to be an as equally well-suited substrate for enzymic attack as arachidonic acid.