Rationale: Obstructive sleep apnea (OSA) is associated with cardiovascular morbidity and mortality, although the underlying mechanisms are not well understood. Objectives:We aimed to determine whether more severe OSA, measured by the Respiratory Disturbance Index (RDI), is associated with subclinical myocardial injury and increased myocardial wall stress. Methods: A total of 1,645 participants (62.5 6 5.5 yr and 54% women) free of coronary heart disease and heart failure and participating in both the Atherosclerosis Risk in the Communities and the Sleep Heart Health Studies underwent overnight polysomnography andmeasurementof high-sensitivity troponinT(hs-TnT) andN-terminal pro B-type natriuretic peptide (NT-proBNP). Measurements and Main Results: OSA severity was defined using conventional clinical categories: none (RDI < 5), mild (RDI 5-15), moderate (RDI 15-30), and severe (RDI . 30). Hs-TnT, but not NTproBNP, was associated with OSA after adjusting for 17 potential confounders (P = 0.02). Over a median of 12.4 (interquartile range, 11.6-13.1) years follow-up, hs-TnT was related to risk of death or incidentheart failure in allOSAcategories (P<0.05 in each category). Conclusions: In middle-Aged to older individuals, OSA severity is independently associated with higher levels of hs-TnT, suggesting that subclinical myocardial injury may play a role in the association between OSA and risk of heart failure. OSA was not associated with NT-proBNP levels after adjusting for multiple possible confounders. Copyright © 2013 by the American Thoracic Society.