We have shown previously that tyrosine 319 in a conserved YIPP motif in the C terminus of angiotensin II (Ang II) type 1 receptors (AT(1)Rs) is essential for transactivation of epidermal growth factor receptor (EGFR) in vitro. We hypothesized that the signaling mechanism mediated through the specific amino acid sequence in the G protein-coupled receptor plays an important role in mediating cardiac hypertrophy in vivo. Transgenic mice with cardiac-specific overexpression of wild-type AT(1)R (Tg-WT) and an AT(1)R with a mutation in the YIPP motif (Tg-Y319F) were studied. Tg-Y319F mice developed no significant cardiac hypertrophy, in contrast to the significant development of hypertrophy in Tg-WT mice. Expression of fetal-type genes, such as atrial natriuretic factor, was also significantly lower in Tg-Y319F than in Tg-WT mice. Infusion of Ang II caused an enhancement of hypertrophy in Tg-WT mice but failed to induce hypertrophy in Tg-Y319F mice. Left ventricular myocardium in Tg-Y319F mice developed significantly less apoptosis and fibrosis than that in Tg-WT mice. EGFR phosphorylation was significantly inhibited in Tg-Y319F mice, confirming that EGFR was not activated in Tg-Y319F mouse hearts. In contrast, activation/phosphorylation of protein kinase C, STAT3, extracellular signal-regulated kinase, and Akt and translocation of Galphaq/11 to the cytosolic fraction were maintained in Tg-Y319F hearts. Furthermore, a genetic cross between Tg-WT and transgenic mice with cardiac-specific overexpression of dominant negative EGFR mimicked the phenotype of Tg-Y319F mice. In conclusion, overexpression of AT(1)-Y319F in cardiac myocytes diminished EGFR transactivation and inhibited a pathological form of cardiac hypertrophy. The YIPP motif in the AT(1)R plays an important role in mediating cardiac hypertrophy in vivo.