Background: and Objective: Obstructive sleep apnea (OSA) is increasingly recognized as a risk factor for cardiovascular diseases. However, long-term population-based evidence across a broad range of cardiovascular outcomes, particularly conduction system disorders, remains limited. We investigated the 15-year cardiovascular outcomes in patients with OSA using a large-scale nationwide cohort. Methods: This retrospective cohort study used the Korean National Health Insurance Service database, including 547,749 patients diagnosed with OSA and 2,282,415 matched controls between 2002 and 2020. Following exclusion criteria and 1:1 propensity score matching, 541,812 individuals were included in each group. The primary outcomes were incidence of atrial fibrillation (AF), premature beats, ventricular arrhythmias, atrioventricular (AV) block, sinus node dysfunction, heart failure, ischemic heart disease (IHD), and stroke. Cumulative incidence was assessed using Kaplan-Meier survival curves. Hazard ratios (HRs) were estimated using Cox proportional hazards models adjusted for relevant covariates. Results: Over a 15-year follow-up period, the OSA group exhibited significantly higher incidence rates for all cardiovascular outcomes than controls. In the matched cohort, adjusted HR were elevated for AF (1.82 [1.77–1.87]), premature beats (2.25 [2.17–2.34]), ventricular arrhythmias (1.81 [1.64–1.99]), AV block (1.81 [1.64–1.99]), sinus node dysfunction (2.22 [1.96–2.50]), heart failure (1.43 [1.39–1.48]), IHD (1.54 [1.52–1.56]), and stroke (1.20 [1.18–1.22]) (all P < 0.0001). Conclusions OSA was independently associated with an increased long-term risk of various cardiovascular outcomes, including arrhythmias, ischemic events, and conduction system disorders. This supports the importance of early identification and longitudinal management of cardiovascular risk in this population.