What is Atrial Fibrillation?
The human heart has two upper chambers and two lower chambers. The upper chambers are called the left atrium and the right atrium - the plural of atrium is atria. The two lower chambers are the the left ventricle and the right ventricle. When the two upper chambers - the atria - contract at an excessively high rate, and in an irregular way, the patient has atrial fibrillation.