Current methods of gene transfer for heart disease include injection into heart muscle or intracoronary coronary delivery, approaches that typically provide limited expression and are cumbersome to apply. To circumvent these problems, we selected a transgene, insulin-like growth factor-I (IGF-I), which may, in theory, have favorable effects on heart function when secreted from a remote site. We examined the feasibility and efficacy of skeletal muscle injection of adeno-associated virus 5 encoding IGF-I under Tet regulation (AAV5.IGFI-tet) to treat heart failure. Myocardial infarction (MI) was induced in rats by coronary occlusion; 1 week later, rats with impaired left ventricular (LV) function received 2×10(12) genome copies (GC) of AAV5.IGFI-tet in the anterior tibialis muscle, and 4 weeks later, were randomly assigned to receive doxycycline in drinking water to activate IGF-I expression (IGF-On; n=10), or not to receive doxycycline (IGF-Off; n=10). Ten weeks after MI (5 weeks after activation of IGF-I expression), LV size and function were assessed by echocardiography and physiological studies. IGF-On rats showed reduced LV end-systolic dimension (p=0.03) and increased LV ejection fraction (p=0.02). In addition, IGF-On rats showed, before and during dobutamine infusion, increases in cardiac output (p=0.02), stroke work (p=0.0001), LV + dP/dt (p<0.0001), LV relaxation (LV - dP/dt; p=0.03), and systolic arterial blood pressure (p=0.0003). Mean arterial pressure and systemic vascular resistance were unchanged. Activation of IGF-I expression reduced cardiac fibrosis (p=0.048), apoptosis (p<0.0001), and caspase-3/7 activity (p=0.04). Serum IGF-I was increased 5 weeks after transgene activation (p=0.008). These data indicate that skeletal muscle injection of AAV5.IGFI-tet enables tetracycline-activated expression, increases serum IGF-I levels, and improves function of the failing heart.