Arrhythmias are uncoordinated or uneven beats of the heart muscle. They're caused by a problem in the electrical system of the heart. Some are harmless and won't cause problems. Others will cause more problems and will need to be treated.

The heart has 4 chambers:

• Two upper chambers (atria) —Get blood from the body and lungs. Then, the blood is pushed into the ventricles.
• Two lower chambers (ventricles) —Get blood from the upper chambers and pump blood to the lungs or out to the body. The left side is the strongest chamber in the heart. It pumps blood to the whole body.

The chambers need to beat in a certain way. This helps the heart to move blood all over the body. A nerve signal keeps the heart beating at 60 to 100 beats a minute.

The nerve excites the heart in a certain pattern. The relaxed atria fill with blood. Then, the signal forces them to contract. This pushes blood into the relaxed ventricles. As the signal moves down, the ventricles contract, pushing blood out to the lungs or body. At the same time, the atria relax and fill with blood. The cycle repeats with each heartbeat.

Heartbeat: Anatomy of the Heart

The electrical signal starts in the sinoatrial (SA) node in the right atrium.

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Arrhythmias cause problems with the timing of beats between the chambers. They can also interfere with how fast or strong the beats are. This may cause:

• Bradycardia —Heartbeat less than 60 beats a minute.
• Tachycardia —Heartbeat more than 100 beats a minute. Brief rises in heartbeat are a normal reaction to physical activity. This helps supply more oxygen to working muscles. Tachycardia that isn't in response to physical activity can cause problems or be a sign of problems.
• Extra beats
• Skipped beats