What is atrial fibrillation (A fib)?

Atrial fibrillation is the most common rhythm problem of the heart. It affects the top chambers of the heart. It's an abnormal, fast rhythm of the top chambers where there's multiple short-circuits all zipping around the top chambers at the same time. It causes the heart to be very rapid, causes it to be very irregular, and often time people are very symptomatic with those rhythm problems.