Protease activated receptor-2 (PAR-2) derived cycloxygenase-2 (COX-2) was recently implicated in a cardiac mast cell and fibroblast cross-talk signaling cascade mediating myocardial remodeling secondary to mechanical stress. We designed this study to investigate in vitro assays of isolated adult cardiac fibroblasts to determine whether binding of tryptase to the PAR-2 receptor on cardiac fibroblasts will lead to increased expression of COX-2 and subsequent formation of the arachodonic acid metabolite 15-dProstaglandin J 2 (15-d-PGJ 2 ). The effects of tryptase (100 mU) and co-incubation with PAR-2 inhibitor peptide sequence FSLLRY-NH 2 (10 -6 M) on proliferation, hydroxyproline concentration, 15-d-PGJ 2 formation and PAR-2/ COX-2 expression were investigated in fibroblasts isolated from 9 week old SD rats. Tryptase induced a significant increase in fibroproliferation, hydroxyproline, 15-d-PGJ 2 formation and PAR-2 expression which were markedly attenuated by FSLLRY. Tryptase-induced changes in cardiac fibroblast function utilize a PAR-2 dependent mechanism.