The heart is, in the simplest terms, a pump made up of muscle tissue. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the heart chambers.
An electrical stimulus is generated in a specialized part of the heart muscle called the sinus node (also called the sinoatrial node, or SA node). The sinus node is a small mass of specialized tissue located in the right atrium (right upper chamber of the heart). In an adult, the sinus node generates an electrical stimulus regularly at 60 to 100 times per minute. This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart's lower chambers (or ventricles) to contract and pump out blood. The right and left atria are stimulated first and contract to push blood from the atria into the ventricles. The ventricles then contract to push blood out into the blood vessels of the body.
The original electrical impulse travels from the sinus node to the atrioventricular node (also called AV node), located between the atria and the ventricles. In the AV node, the impulses are slowed down for a very short period, allowing the atria to contract a fraction of a second before the ventricles. The blood from the atria empties into the ventricles before the ventricles contract. After passing through the AV node, the electrical current then continues down the conduction pathway, via a pathway called the bundle of His, and into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to the right and left ventricles.
Normally at rest, as the electrical impulse moves through the heart, the heart contracts about 60 to 140 times a minute depending on a person's age. In general, your heart rate slows as you age.
Under some abnormal conditions, certain heart tissue is capable of starting a heartbeat, or becoming the "pacemaker," just like the sinus node. An arrhythmia (abnormal heartbeat) may occur when:
The heart's natural pacemaker (the sinus node) develops an abnormal rate or rhythm.
The normal conduction pathway is interrupted.
Another part of the heart takes over as pacemaker.
Symptoms of an arrhythmia can include heart palpitations, shortness of breath, dizziness, or fainting.
Your doctor may do an ECG (electrocardiogram) to evaluate the rhythm of the heart. This is a painless test that involves recording the electrical activity of your heart with several small stickers attached to your chest. If the electrical rhythm is abnormal, medication or surgery may be needed.