It is not known whether the metabolic syndrome is associated with poor exercise capacity among patients who have established coronary heart disease. We evaluated the association of the metabolic syndrome with treadmill exercise capacity and heart rate recovery among patients who had coronary heart disease. We measured treadmill exercise capacity (METs) and heart rate recovery (beats per minute) in 943 subjects who had known coronary heart disease. Of these, 377 (40%) had the metabolic syndrome as defined by criteria of the National Cholesterol Education Program. Participants who had the metabolic syndrome were more likely to have poor exercise capacity (METs <5, 33% vs 18%, p <0.0001) and poor heart rate recovery (<or=16 beats/min, 34% vs 21%, p <0.0001) than those who did not have the metabolic syndrome. In ordinal logistic regression analyses, the metabolic syndrome was associated with decreased exercise capacity (odds ratio [OR] 2.2, 95% confidence interval [CI] 1.7 to 2.8, p <0.0001) and decreased heart rate recovery (OR 1.8, 95% CI 1.4 to 2.3, p <0.0001). These associations remained strong after adjusting for potential confounding variables (OR 1.6, 95% CI 1.2 to 2.1, p = 0.003 for decreased exercise capacity; OR 1.4, 95% CI 1.1 to 1.9, p = 0.02 for decreased heart rate recovery). The metabolic syndrome is independently associated with poor exercise capacity and poor heart rate recovery in patients who have established coronary heart disease. Decreased exercise capacity may contribute to the adverse outcomes associated with the metabolic syndrome.