Myofibroblasts respond to an array of signals from mitogens and cytokines during the course of wound healing following a myocardial infarction (MI), and these signals may coordinate ventricular myofibroblast proliferation. Further, myofibroblasts are contractile and contribute to wound contraction by imparting mechanical tension on surrounding extracellular matrix. While TGF-₁, CT-1 and PDGF-BB participate in various stages of post-MI wound healing, their combined net effect(s) on myofibroblast function is unknown. We investigated myofibroblast proliferation, expression of cell cycle proteins, and contractile function of cells treated with either TGF-₁and/or CT-1. We confirmed that TGF-₁ (10 ng/ml) suppresses proliferation of these cells while CT-1 (10 ng/ml) and, for comparative purposes, PDGF-BB (1ng/ml) treatments were associated with proliferation. Specific TGF-₁ treatment ablated CT-1 - induced myofibroblast proliferation. TGF-₁ effects were specific as they were supressed by either TGF- neutralizing antibody or viral Smad7 overexpression. TGF-₁treatment also increased expression of p27 and decreased expression of cyclin E and cdk2 in primary cells. CT-1 (10 ng/ml) treatment of myofibroblasts had no effect on collagen gel deformation vs controls while TGF-₁ (10 ng/ml) and PDGF (10 ng/ml) treatments were associated with significant cell contraction; again, TGF-₁-mediated contraction was unaffected by CT-1. Alone, CT-1 and TGF-₁ treatments exert opposing effects on myofibroblast function while in combination, TGF-₁-mediated effects supercede those of CT-1 (and PDGF-BB). Thus TGF-₁and CT-1 exert differential effects on myofibroblast proliferation and contraction in vitro and we suggest that a balance of these effects may be important for the execution of normal cardiac wound healing.