Background: The routine administration of supplemental oxygen to non-hypoxic patients with acute myocardial infarction has been abandoned for lack of mortality benefit. However, the benefits of continuous positive airway pressure (CPAP) use in patients hospitalized with acute cardiovascular disease and concomitant obstructive sleep apnea (OSA) remain to be elucidated. Methods: Using ICD-10-CM codes, we searched the 2016-2019 Nationwide Inpatient Sample for patients diagnosed with unstable angina, acute myocardial infarction (AMI), acute decompensated heart failure (ADHF), and atrial fibrillation with rapid ventricular response (AFRVR), who also carried a diagnosis of OSA. We identified in-hospital CPAP use with ICD-10-PCS codes. In-hospital death, length of stay (LOS) and hospital charges were compared between patients with and without OSA, and between OSA patients with and without CPAP use. Results: Our sample included 2,959,991 patients, of which 1.5% were diagnosed with UA, 30.3% with AMI, 37.5% with ADHF, and 45.8% with AF. OSA was present in 12.3%. Patients with OSA were more likely to be younger, male, smokers, obese, have chronic obstructive pulmonary disease, renal failure, and heart failure (p < 0.001 for all). Patients with OSA had significantly lower in-hospital mortality (aOR: 0.71, 95% CI [0.7-0.73]). Among patients with OSA, CPAP use significantly increased the odds of in-hospital death (aOR: 1.51, 95% CI [1.44-1.60]), LOS (adjusted mean difference of 1.49 days, 95% CI [1.43, 1.55]), and hospital charges (adjusted mean difference of $1168, 95% CI [273, 2062]). Conclusion: Our study showed that patients with recognized OSA and hospitalized for AMI, ADHF or AFRVR, who were not treated with CPAP, had significantly lower in-hospital mortality and resource utilization. Keywords: Myocardial infarction, Obstructive sleep apnea, Heart failure, Atrial fibrillation, Ischemic preconditioning