Myocardial infarction (MI) results in left ventricular remodeling (e.g., ventricular hypertrophy, dilatation and fibrosis). Fibrosis, contributes to increased myocardial stiffening, impaired ventricular filling and function and reduced cardiac output. Adenylyl cyclase (AC) expression and activity are reduced in animal models of heart failure. Stimulation of AC can inhibit extracellular matrix production in isolated cardiac fibroblasts; however, a role for reduced AC expression and activity in fibrosis associated with cardiac remodeling after chronic MI has never been determined. We tested the hypothesis that AC expression and activity are reduced in cardiac fibroblasts after chronic (18 week) MI. Rats underwent coronary artery ligation or sham surgery (Con) and echocardiography was used to assess left ventricular remodeling 1, 3, 5, 7, 10, 12 and 18 weeks after surgery. Cardiac fibroblasts were isolated from the non-infarcted myocardium and compared for differences in AC activity and collagen synthesis. End-diastolic dimension was increased (Con: 0.76 ± 0.02 (SEM) cm, MI: 1.0 ± 0.02 cm; p<0.001) and fractional shortening decreased (Con: 44 ± 2%, MI: 17 ± 2%; p<0.001) in MI compared to control rats. Basal and forskolin-stimulated cAMP production were decreased by 90% and 93%, respectively, and AC5/6 expression was decreased 39% in fibroblasts isolated from MI rats compared to sham controls. Serum-stimulated collagen production was increased 2-fold and forskolin-mediated inhibition of collagen synthesis was reduced in fibroblasts from MI rats compared to controls. Our data demonstrate that AC expression and activity are reduced and collagen production is increased in cardiac fibroblasts of rats after MI.