This study aims to identify how many patients who have atrial fibrillation, also have sleep apnoea. This is important because sleep apnoea can be a trigger to atrial fibrillation and it can be corrected with a simple intervention. Therefore it is important to understand its prevalence (how many patients with atrial fibrillation are affected by it). Also, obesity and sleep disorders are often associated, therefore the evolution of atrial fibrillation is studied in patients who also have obesity and have lost weight compared with patients who did not loose any weight or are not obese. As medications or therapy are not changed, this is an observational study.

Inclusion Criteria primary outcome:

• 1 episode of atrial fibrillation in the previous year

Inclusion Criteria secondary outcome:

• BMI > o = 27Kg/m2
• AHI >30 o con 15\

patients between 18 and 75 years of age, male and female, who come to the study centre between January 2019 and January 2023 with a diagnosis of atrial fibrillation and a recurrence (or first episode) in the previous year and who can undergo polysomnography