ObjectiveTo analyze the causal relationship between obstructive sleep apnea (OSA) with its typical symptoms (daytime sleepiness and snoring) and cardiovascular diseases (hypertension, coronary heart disease, myocardial infarction, heart failure) by using Mendelian randomization. MethodsWe used the instrumental variables (IV) in the FINNGen database and the UK Biobank to perform two-sample Mendelian randomization (TSMR) analysis. The results of random-effects inverse variance weighting method (IVW) were the main results. MR-Egger method was used for pleiotropic analysis and sensitivity analysis was performed by the leave-one-out method to verify the reliability of the data. ResultsOSA could lead to hypertension (IVW β=0.043, 95%CI 0.012 to 0.074, P=0.006) and heart failure (IVW β=0.234, 95%CI 0.015 to 0.452, P=0.036). Daytime sleepiness also had a pathogenic effect on heart failure (IVW β=1.139, 95%CI 0.271 to 2.006, P=0.010). There was no causal association between OSA and CHD or MI, snoring and the four CVDs. There was no causal association between daytime sleepiness and hypertension, CHD or MI.ConclusionOSA and daytime sleepiness have pathogenic effects on hypertension and heart failure, with heart failure being the most affected.