BACKGROUND Chronotropic incompetence and left ventricular (LV) dilatation have both been shown to be markers of an adverse cardiovascular prognosis. Chronotropic incompetence has been described in patients with symptomatic LV dilatation and dysfunction, but the effect of asymptomatic LV dilatation and hypertrophy on exercise heart rate response has not been well characterized. RESULTS Members of the Framingham Offspring Study underwent M-mode echocardiography and graded exercise testing as part of a routine evaluation. Subjects receiving beta-blockers and digitalis and subjects with preexisting coronary heart disease, heart failure, and baseline ST-segment abnormalities were excluded. Chronotropic incompetence was assessed in 2 ways: (1) failure to achieve an age--predicted target heart rate and (2) a low chronotropic index, a measure of heart rate response that takes into account effects of age, resting heart rate, and physical fitness. Echocardiographic variables studied included LV diastolic and systolic dimensions, LV wall thickness, LV mass, and fractional shortening. There were 1414 men and 1601 women eligible for analyses; failure to reach target heart rate occurred in 20% of men and 23% of women; a low chronotropic index was noted in 14% of men and 12% of women. In unadjusted categorical analyses, an abnormally high LV mass, as defined by exceeding the 90th percentile predicted value of a healthy reference group, was associated with failure to achieve target heart rate in men (31% vs 18%, odds ratio [OR] 2.05, 95% confidence interval [CI] 1.49 to 2.83) and women (34% vs 20%, OR 2.09, 95% CI 1.63 to 2.69). Similarly, an abnormally high LV mass was predictive of a low chronotropic index in men (18% vs 13%, OR 1. 47, 95% CI 1.01 to 2.14) and women (17% vs 10%, OR 1.78, 95% CI 1.29 to 2.45). When considered as a continuous variable, LV diastolic dimension predicted failure to achieve target heart rate in men (ageadjusted OR for 1 SD increase 1.30, 95% CI 1.00 to 1.33) and in women (age-adjusted OR 1.30, 95% CI 1.12 to 1.50). Similarly, LV diastolic dimension predicted low chronotropic index in men (age-adjusted OR 1.22, 95% CI 1.05 to 1.42) and in women (age-adjusted OR 1.18, 95% CI 1.01 to 1.39). After also adjusting for resting blood pressure, physical activity, and other potential confounders, LV mass, when considered as a continuous variable, remained predictive of failure to achieve target heart rate in men (adjusted OR 1.23, 95% CI 1.06 to 1.42) and a low chronotropic index in men (adjusted OR 1.26, 95% CI 1.06 to 1.49). Among women, LV diastolic dimension predicted failure to achieve target heart rate (adjusted OR 1.27, 95% CI 1.12 to 1.45) and low chronotropic index (adjusted OR 1.18, 95% CI 1.01 to 1.39), whereas in men it predicted low chronotropic index (adjusted OR 1.22, 95% CI 1.04 to 1.42). CONCLUSIONS In this asymptomatic, population-based cohort, chronotropic incompetence was predicted by increased LV mass and cavity size; among men, it was also predicted by depressed systolic function.