Cardiac fibrosis is a pathological process associated with development of heart failure. TGF-β and WNT signaling have been implicated in pathogenesis of cardiac fibrosis, however little is known about molecular cross-talk between these two pathways. The aim of this study was to examine the effect of exogenous canonical WNT3a and non-canonical WNT5a in TGF-β-activated human cardiac fibroblasts. We found that WNT3a and TGF-β induced -catenin-dependent response, whereas WNT5a prompted AP-1 activity. TGF-β triggered profibrotic signature in cardiac fibroblasts, and co-stimulation with WNT3a or co-activation of the β-catenin pathway with GSK3β inhibitor CHIR99021 enhanced collagen I and fibronectin production and development of active contractile stress fibers. In the absence of TGF-β, neither WNT3a nor CHIR99021 exerted profibrotic response. On a molecular level, in TGF-β-activated fibroblasts WNT3a enhanced phosphorylation of TAK1 and production and secretion of IL-11 but showed no effect on Smad pathway. Neutralization of IL-11 activity with the blocking anti-IL-11 antibody effectively reduced profibrotic response of cardiac fibroblasts activated with TGF-β and WNT3a. In contrast to canonical WNT3a, co-activation with non-canonical WNT5a suppressed TGF-β-induced production of collagen I. In conclusion, WNT/β-catenin signaling promotes TGF-β-mediated fibroblast-to-myofibroblast transition by enhancing IL-11 production. Thus, the uncovered mechanism broadens our knowledge on molecular basis of cardiac fibrogenesis and defines novel therapeutic targets for fibrotic heart diseases.