Normally, the heart pumps in a well-timed fashion. The two upper chambers (atria) contract first followed by the two lower chambers (ventricles). This coordinated pumping is powered by the heart's own electrical system and efficiently pumps blood throughout the body. In atrial fibrillation (AF), a type of arrhythmia, the electrical signals fire rapidly and chaotically. This causes the atria to quiver instead of contracting normally. Many of the signals also reach the ventricles, causing them to contract irregularly too. This results in a fast and irregular heart rhythm. Over time, this can weaken the heart and lead to heart failure. Plus, when the atria do not contract effectively, the blood may pool in the heart. This increases the risk that a blood clot may form and travel to the brain, causing a stroke. People with AF are 5 to 7 times more likely to have a stroke than people who do not have AF. This condition is also more common in people who are over 65 and is seen more often in men than women.
AF can develop when someone has underlying valvular heart disease, has had a heart attack, or suffers heart failure. High blood pressure, thyroid problems, alcoholism, sleep apnea and certain lung diseases can also be contributing factors.