Abstract: . . .  the left side of the heart, and the two left chambers pump this oxygenated blood to the rest of the body. The lower (major) pumping chambers, called the ventricles, receive blood from the top chambers, the atria, and do the hard work of pumping the blood to the other parts of the body. In a normal heart, the atria contract (squeeze) first, pushing blood into the ventricles. The ventricles then contract; the right ventricle pumping the blood out to the lungs and the left ventricle pumping blood to the rest of the body. This process repeats at a regular rate, usually around 60 to100 times every minute. Normally, the contraction of the atria is set off by tiny electrical signals that come from the hearts natural pacemaker a small area of the heart called the sinus node that is located in the top of the right atrium. These signals travel rapidly throughout the atria to ensure that all the muscle fibres contract at the same time, pushing blood into the ventricles. These same electrical signals are passed on to the ventricles via the atrioventricular (AV) node and cause the ventricles to contract a short time later, after they have been filled with blood from the atria. This normal heart rhythm is known as sinus rhythm, because it is controlled by the sinus node. Normal electrical control of the heart beat Page 3 3. What happens in atrial fibrillation ? AF occurs when there are abnormal electrical impulses in the upper chambers of the heart (the atria). In AF, waves of uncontrolled electrical signals travel through the atria, rather than the normal, highly regulated signals from the sinus node. These waves often start in one or more of the four veins that bring blood from the lungs into the heart (the pulmonary veins). These signals cause the muscle fibres in the atria to contract out of time with each other, and the atria quiver (or, in medical terms, fibrillate). Some of this abnormal electrical activity is passed on to the ventricles, causing a rapid and irregular heartbeat. When the heart is in AF, it is not pumping regularly, and therefore not working as efficiently as it should be. What are the symptoms of AF? People with AF may experience palpitations that is, become aware of their heartbeat, and may actually feel irregular fluttering of the heart. This fluttering is caused by the abnormal electrical signals in the atria reaching the ventricles and causing them to beat too rapidly and in an irregular pattern. Some people may notice that they have an irregular pulse. AF may also cause general feelings of fatigue, weakness, exercise intolerance, discomfort or dizziness, because the heart is not pumping efficiently. Occasionally this may result in fainting or collapse. Some people with . . .
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