Conditions in which the heart is considered to be the cause of atrial fibrillation are:

1. Heart valve disease: each heart has four valves that separate upper and lower parts of the heart. Disease in some of these valves may cause atrial fibrillation.
2. Enlargement of the heart for any reason may cause atrial fibrillation. Elevated blood pressure, congenital heart disease (heart problems you were born with), weakness of the muscles of the heart, and heart attack are among situations that can enlarge the heart.
3. Inflammation of the sac that covers the heart. Viral infections, radiation therapy in the chest area, some rare bacterial infections, and even trauma to the chest like a motor-vehicle accident can cause inflammation of the sac that covers the heart and that inflammation may cause atrial fibrillation.
4. Narrowness of the vessels that bring blood to the heart can weaken heart muscles and cause atrial fibrillation.
5. A condition known as "Sick Sinus Syndrome" (a kind of "laziness" of the center in the heart that is responsible for starting the electrical impulse in the heart that causes it to beat).
6. Obesity is typically associated with diabetes, hypertension and obstructive sleep apnea which in turn can cause AFib.
7. Genetic inheritance: A family history of AF increases risk by 30%.Various genetic mutations may be responsible. There is a lot of new information that is being published linking genetic mutations as causative factors for AFib.

Conditions in which the heart is not the primary cause of atrial fibrillation:

1. Disease of thyroid gland: your thyroid gland is located in the neck. Unfortunately in most people, disease of thyroid does not have any manifestation in the neck area. It may show up as a change in appetite, a change in weight, inability to tolerate cold or heat, constipation or diarrhea, changes in skin and hair, change in menstruation and sexual desire, sleepiness and a lot of other non-specific findings. Atrial fibrillation can also happen when thyroid is overactive.
2. Disease of the lungs: your heart and lungs are very close, both because of their location in your body and their work. Some diseases of the lung like pneumonia, a blood clot in the lung (called a pulmonary embolism), asthma, and conditions due to smoking (COPD) can cause atrial fibrillation.
3. Infections, in any part of body, especially in older age can cause atrial fibrillation.
4. Drinking too much alcohol (known as holiday heart) and caffeine can trigger atrial fibrillation.
5. Electrolyte abnormality: Your body needs certain substances such as salt and potassium, called electrolytes, which help control your heart beat. An abnormality in the levels of these electrolytes in your blood can cause different forms of arrhythmias including atrial fibrillation.
6. Toxic effect of some medications.
7. Tumors, or bleeding in the brain, or stroke.

No underlying heart disease is found in at least 8-10 % patients who have AFib. In these cases, AFib may be related to alcohol or excessive caffeine use, stress, certain recreational and non prescription drugs, herbal supplements, electrolyte or metabolic imbalances, or severe infections. In some cases, no cause can be found.

The risk of AF increases with age, particularly after age 60. The incidence of AFib dramatically increases with each decade from that point.