Atrial fibrillation (AF) is the most common sustained cardiac rhythm disorder. Obstructive sleep apnea (OSA), is four times more common among patients with AF than without. OSA has been associated with a greater recurrence rate of AF after initially successful treatment of AF and treatment of OSA reduces recurrence of AF. To identify the underlying mechanisms, we aim to determine effects of OSA on atrial electrical activation and to characterize sleep apnea in AF patients in a more precise way.