This study utilized a transgenic mouse model that expresses an inducible dominant-negative mutation of the transforming growth factor (TGF)-β type II receptor (DnTGFβRII) to define the structural and functional responses of the left ventricle (LV) to pressure-overload stress in the absence of an intact TGF-β signaling cascade. DnTGFβRII and nontransgenic (NTG) control mice (male, 8-10 wk) were randomized to receive Zn2+ (25 mM ZnSO4 in drinking H2O to induce DnTGFβRII gene expression) or control tap H2O and then further randomized to undergo transverse aortic constriction (TAC) or sham surgery. At 7 days post-TAC, interstitial nonmyocyte proliferation (Ki67 staining) was greatly reduced in LV of DnTGFβRII+Zn2+ mice compared with the other TAC groups. At 28 and 120 days post-TAC, collagen deposition (picrosirius-red staining) in LV was attenuated in DnTGFβRII+Zn2+ mice compared with the other TAC groups. LV end systolic diameter and end systolic and end diastolic volumes were markedly increased, while ejection fraction and fractional shortening were significantly decreased in TAC-DnTGFβRII+Zn2+ mice compared with the other groups at 120 days post-TAC. These data indicate that interruption of TGF-β signaling attenuates pressure-overload-induced interstitial nonmyocyte proliferation and collagen deposition and promotes LV dilation and dysfunction in the pressure-overloaded heart, thus creating a novel model of dilated cardiomyopathy. Copyright © 2010 the American Physiological Society.