Atrial fibrillation (also called AF or A-Fib) is the most common type of irregular heartbeat, occurring in 1-2% of the general population. However, it is a problem that increases with age, with approximately 5-15% of people between 80-90 years of age affected. There is also an increased risk of atrial fibrillation among people with heart conditions, including irritation of the membrane surrounding the heart (pericarditis), heart muscle disease (cardiomyopathy), abnormal heart valves or congenital heart defects.