OBJECTIVE:Studies addressing the association between a reduced drop of heart rate (HR) at night with subclinical organ damage and cardiovascular events in the general population are scanty. We evaluated this issue in subjects enrolled in the Pressioni Monitorate E Loro Associazioni (PAMELA) study. DESIGN AND METHOD:At entry 2,021 subjects underwent diagnostic tests including laboratory investigations, 24-h ambulatory blood pressure (BP) monitoring and echocardiography. Participants were followed from the initial medical visit for a time interval of 148 ± 27 months. To explore the association of circadian HR rhythm and outcomes participants were classified in the primary analysis according to quartiles of nocturnal HR decrease. In secondary analyses the population was also classified according non-dipping nocturnal HR (defined as a drop in average HR at night lower than 10% compared to day-time values) and next in four categories(1) BP/HR dipper, 2) BP/HR non dipper, 3) HR dipper/BP non dipper, 4) HR non dipper/BP dipper). RESULTS:A flattened circadian HR rhythm (i.e. lowest quartile of night-time HR dip) was independently associated to left atrial (LA) enlargement, but not to left ventricular hypertrophy; moreover, it was predictive of fatal and non-fatal cardiovascular events, independently of several confounders (hazard ratio 1.8, CI1.13–2.86, p < 0.01 vs highest quartile). CONCLUSIONS:A blunted dipping of nocturnal HR is associated to preclinical cardiac damage in terms of LA enlargement and is predictive cardiovascular morbidity and mortality in the general population.