An arrhythmia, or irregular heartbeat, is a problem with the rate or rhythm of the heartbeat. People with this condition may have a heart that beats too quickly, too slowly or has an irregular rhythm. While it is normal to feel as if your heart skips a beat occasionally, a frequent irregular rhythm may lead to palpitations, dizziness and other symptoms, according to the National Heart, Lung, and Blood Institute (NHLBI).

Arrhythmias may occur when there is a problem with the heart's electrical system. In the case of atrial fibrillation, also known as A-fib or AF, the result is that the top chambers of the heart contract irregularly.

"Atrial fibrillation is the most common arrhythmia," said Dr. Lawrence Phillips, a cardiologist and assistant professor at NYU Langone Medical Center in New York City. "It's caused [by] irregular impulses coming from the top chamber of the heart."

Atrial fibrillation may cause heart disease or worsen existing heart disease, according to the NHLBI. Sometimes it goes away on its own. For others, atrial fibrillation is an ongoing heart problem that lasts for years.

What are the causes of atrial fibrillation?

The human heart is made up of four chambers: The left and right atria and the left and right ventricles. The electrical signals that control the heartbeat originate in the right atrium, at a spot called the sinus node. This node pulses out an electrical signal, which spreads from the top of the heart to the bottom, causing the muscle to contract as it travels, according to the National Institutes of Health (NIH).

The path of this electrical stimulation is important, as it causes blood to move in the proper direction at the proper time. First, the atria contract, sending blood into the ventricles. Next, the signal hits another node, the atrioventricular node, which slows the electrical pulse slightly so the ventricles can finish filling. Then the electrical signal zips down the ventricles, causing them to contract and squeezing blood out of the heart. Oxygenated blood from the left ventricle goes out to the body's tissues, while deoxygenated blood from the right ventricle goes to the lungs to pick up more oxygen.

This process repeats 60 to 100 times a minute, depending on the person's fitness and pulse rate.

In atrial fibrillation, this electrical signal is disrupted. Instead of spreading normally through the atria, the electrical pulse spreads erratically. "When they beat erratically, it can make the heart go fast," Phillips said. This causes fibrillation, or rapid and irregular contraction.

The erratic signals also arrive at the atrioventricular node in a disorganized way, causing the ventricles to beat faster than normal. The atria and ventricles are now uncoordinated, so that blood doesn't move in and out of the heart efficiently.