BACKGROUND An analysis of cardiac injury markers in patients with OSA who sustain an episode of acute coronary syndrome (ACS) may contribute to a better understanding of the interactions and impact of OSA in subjects with ACS. We compared peak cardiac troponin I (cTnI) levels in patients with OSA and patients without OSA who were admitted for ACS. METHODS Blood samples were collected every 6 hours from the time of admission until two consecutive assays showed a downward trend in the cTnI assay. The highest value obtained defined the peak cTnI value, which provides an estimate of infarct size. RESULTS We included 89 patients with OSA and 38 patients without OSA with an apnea-hypopnea index of a median of 32 (interquartile range [IQR], 20.8-46.6/h and 4.8 [IQR, 1.6-9.6]/h, respectively. The peak cTnI value was significantly higher in patients without OSA than in patients with OSA (median, 10.7 ng/mL [IQR, 1.78-40.1 ng/mL] vs 3.79 ng/mL [IQR, 0.37-24.3 ng/mL]; P = .04). The multivariable linear regression analysis of the relationship between peak cTnI value and patient group, age, sex, and type of ACS showed that the presence or absence of OSA significantly contributed to the peak cTnI level, which was 54% lower in patients with OSA than in those without OSA. CONCLUSIONS The results of this study suggest that OSA has a protective effect in the context of myocardial infarction and that patients with OSA may experience less severe myocardial injury. The possible role of OSA in cardioprotection should be explored in future studies.