Atrial fibrillation (AF) is the most common rhythm disorder and involves an increased risk of cardiovascular disease and death, impaired quality of life and a high proportion of healthcare consumption. An important risk factor is obstructive sleep apnea (OSA). However, it is not fully understood why OSA induces AF. It may be due to a proinflammatory state, sympathetic activation and acute changes in blood pressure during apnéas, but few studies are performed. Hypertension with its coherent arterial stiffness is related to all these factors, is common in OSA, and is the most common cause of AF. The cause of AF in hypertensive subjects is believed due to a pressure overloaded left heart, with dilation and fibrosis of the left atrium, promoting the development of AF. Hypertension and arterial stiffness can thus be important triggering factors for AF in OSA. In this project, teh investigators investigate the occurrence of OSA in AF patients. Furthermore, underlying mechanisms for the development and recurrence of AF after intervention in OSA patients are investigated. 300 patients scheduled for AF ablation or cardioversion are invited and examined with sleep registration, 24h blood pressure, aortic stiffness measurement, test of autonomic function, echocardiography, ECG and labs. The patients are followed at months 3, 6 and 12 with 7 days ECG for recurrence. The aim is to give insights into the need for screening for OSA in patients with AF. The study also aim at enabling preventive treatment through better understanding of underlying treatable mechanisms. The results are believed to lead to fewer new AFs, as well as fewer AF recurrences in patients with OSA.