While cardiac hypertrophy elicited by pathological stimuli eventually leads to cardiac dysfunction, exercise-induced hypertrophy does not. This sug-gests that a beneficial hypertrophic phenotype exists. In search of an under-lying molecular substrate we used microarray technology to identify cardiac gene expression in response to exercise. Rats exercised for seven weeks on a treadmill were characterized by invasive blood pressure mea-surements and echocardiography.