Background: In 2022, the American Heart Association (AHA) updated the list of modifiable lifestyle factors most important for cardiovascular health to include sleep. Sleep disturbances, such as insomnia and sleep apnea, have been associated with an increased risk of incident cardiovascular disease (CVD). However, the relationship between sleep duration and mortality remains to be fully elucidated. Methods: We used National Health and Nutrition Examination Survey (NHANES) data linked to National Death Index records to examine the association between sleep duration and CVD and all-cause mortality. A representative sample of 37,975 adults aged ≥20 years participated in the survey, which included assessments of social, behavioral, and metabolic factors, including usual weekday sleep duration. Sleep duration was categorized as (1) ideal (6-<9 hours); (2) insufficient (<6 hours); and (3) excessive (≥9 hours). Cox proportional hazards regression models were used to determine the relationship between sleep duration and CVD and all-cause mortality. Models were adjusted for age, sex, and race. Results: Over an average of 7.5 years of follow-up, 2,406 CVD deaths were confirmed. In adjusted models, compared to ideal sleep duration (6-<9 hours), excessive sleep (≥9 hours) was associated with a 65% increase in CVD mortality (HR = 1.65; 95% CI: 1.39, 1.96), a 53% increase in cerebrovascular disease mortality (HR = 1.53; 95% CI: 1.22, 1.92), and a 52% increase in all-cause mortality (HR = 1.52; 95% CI: 1.40, 1.66). Insufficient sleep (<6 hours) was associated with a 38% increase in CVD mortality (HR = 1.38; 95% CI: 1.08, 1.75) and a 54% increase in all-cause mortality (HR = 1.54; 95% CI: 1.38, 1.71). Conclusion: We found that both insufficient and excessive sleep were associated with increased risk of CVD and all-cause mortality, and the risk was more pronounced for excessive sleep. These findings emphasize the importance of recognizing sleep as a modifiable risk factor for CVD. Further research is needed to explore the relationship between sleep and CVD, including incorporating sleep quality into risk assessments and defining clinically meaningful categorizations of sleep metrics.