The present research is a randomized clinical trial for Determinant of the effects of fish oil supplementation on the adiponectin and ADMA serum levels in patients with chronic atrial fibrillation. The samples of the study will constitute 80 patients with chronic atrial fibrillation including men and women above 50 years with BMI higher than 25 kg/m2 coming to the Shahid Rajaei Heart Center. Exclusion criteria included the following: 1) suffering from hyperthyroidism, 2) disorders of heart valves, and 3) people who started taking in fish oil supplement within the three months to the intervention. Patients will be randomly divided into two groups. At the first meeting the purpose of study will be described and asked them to fill the consent form. Group 1 will receive 2000 mg fish oil capsules for eight weeks and group 2 will receive 2000mg placebo capsules (same shape, colour, size) two times after meal (each time 1capsule including 1000mg . The intake of nutrients will assess through 24-hour questionnaire filled in by the patients before and after treatment. Height, weight and waist circumference, will measure before and after the treatment. Furthermore, fasting blood will be collected and stored at -80 (c) refrigerator before and after the intervention. The serum levels of adiponectin, Asymmetric dimethylarginine, total cholesterol, low density lipoprotein, high density lipoprotein, very low density lipoprotein, triglyceride and fasting blood sugar will measure before and after the intervention.