Cellular redox signalling is in part mediated by post translational modification of proteins by reactive oxygen species, nitrogen species or by products of their reactions. Enhanced lipid peroxidation has traditionally been causatively associated with many diseases; although important roles in redox signalling are now being recognised. Many lipid peroxidation products are reactive and are capable of reacting with and modifying protein thiols. Cyclopentenone prostaglandins (CyPGs) are model examples of reactive oxidised lipids, containing electrophilic carbon centres that allow covalent adduction with target proteins. To determine if lipid-protein adducts form in a cellular setting, a biotinylated derivative of 15-deoxy-delta 12, 14 prostaglandin J2 (15d-PGJ2) (an electrophilic lipid) was used to treat adult rat ventricular myocytes. There was a dose- and time-dependent increase in biotin-15d-PGJ2 labelling which was maximal at 50μM 15d-PGJ2 and after 120 minutes. 15d-PGJ2 treatment of isolated rat hearts decreased coronary perfusion pressure (vasodilation). Mesenteric vessels were treated with biotin-15d-PGJ2 in order to identify proteins that formed an adduct with 15d-PGJ2. These proteins were purified with avidin-agarose and identified by separation of tryptic digests by liquid chromatography with online analysis by mass spectrometry. Several proteins were identified that formed an adduct. However one particular protein that was modified, soluble epoxide hydrolase (sEH), we hypothesized might account for the vasodilation observed in isolated hearts. sEH catalyses the hydroysis of epoxides, such as epoxyeicosatrienoic acids (EETs), to diols (dihydroxyeicosatrienoic acids). We assayed sEH activity, and found 15d-PGJ2 inhibited its activity, both in vitro with recombinant sEH, as well in cardiac homogenates after hearts were exposed to this lipid. Furthermore, when an inhibitor of sEH, (AUDA), was perfused through isolated rat hearts, it mimicked the vasodilatory response of 15d-PJ2. Similarly, 14, 15-epoxyeicosatrienoic acid (14, 15-EET) also decreased coronary perfusion pressure. These results suggest that 15d-PGJ2 is able to form an adduct with sEH, which inactivates it. This results in cellular accumulation of 14, 15-EET, allowing them to exert their vasodilatory response.