The incidence of heart failure in the population increases steeply among older people. Overactivation of the sympathetic nervous system is associated to and responsible for worsening of heart failure. This study describes the influence of aging on short-term left ventricular (LV) adaptation to b-adrenergic stimulation in Wistar rats. In controls at 18 mo, interstitial fibrosis was increased with respect to 3-mo-old rats, whereas myocytes dimension and the messenger RNA (mRNA) abundance of atrial natriuretic peptide (ANP), a2(I) procollagen, transforming growth factor (TGF-b1, TGF-b3), and secreted protein, acidic and rich in cysteine (SPARC) were not different. To determine how aging affects LV adaptation to adrenergic stimulation, two groups of animals received isoproterenol (ISO, 1 mg/kg/d) for 3 days. There was no significant difference between young and older rats with respect to increase in LV weight, myocytes dimension, and mRNA abundance of all the genes considered, except a1(III) procollagen. These findings indicate that despite limited compensatory hypertrophy and higher fibrosis, LV from aged nonsenescent rats preserves the capacity to adapt to b-adrenergic stimulation through the upregulation of several genes encoding extracellular matrix-related proteins.