When the heart is healthy, its own natural pacemaker (the sinoatrial, or SA, node) sends electrical impulses to the heart muscles, telling them when to contract. These contractions pump blood through the heart and out to the rest of the body. Media provided courtesy of Boston Scientific. © 2015 Boston Scientific Corporation or its affiliates. All rights reserved.

The heart is the pump that is responsible for keeping blood circulating throughout your body. The heart is divided into four chambers, the left and right atria and the left and right ventricles. A wall called the septum separates the left side of the heart from the right. The two upper chambers are separated by the thin interatrial septum. The thicker, muscular wall that separates the two lower heart chambers is called the interventricular septum.

The valves, or one-way doors within the heart, separate the atria from the ventricles. The valves carefully regulate blood flow through the heart’s chambers. The walls of the heart and the valves keep the blood on a “one-way street” through the heart and out to the body and back.

When blood arrives at the heart, it comes through veins from the body. Upon arrival at the heart, the blood is depleted of oxygen. It enters the right atrium of the heart. Then the tricuspid valve opens, the blood flows into the ventricle, and the ventricle contracts, forcing the blood through the open pulmonary valve and into the pulmonary artery. The tricuspid valve prevents the blood from flowing backward into the right atrium when the ventricle contracts. The pulmonary artery then carries the blood to the lungs to release carbon dioxide and pick up oxygen.

From the lungs, blood returns to the heart through the pulmonary veins and enters the left atrium. When the mitral valve opens, the blood flows from the left atrium to the left ventricle. Once full, the ventricle contracts, and the blood is forced through the open aortic valve and into the aorta, which is the largest artery in the body. The mitral valve keeps the blood from being pushed backward into the left atrium

The aorta distributes blood to the smaller arteries and other blood vessels that supply your entire body with oxygenated blood. The sound of the closing of the valves of the heart is what makes the “heartbeat” sound everyone knows.

More information about how the heart works can be found here.

When the Heart Doesn’t Beat Correctly

The heart’s natural beating action is stimulated by electrical impulses fired by the heart’s own natural pacemaker, known as the sinoatrial (SA) node, which is located in the top of the right atrium. The electrical impulses travel through the muscles of both atria, encouraging rhythmic contractions.

However, if the SA node misfires, then the heart begins to beat erratically and the atria will quiver. This may create the sensation that many people with atrial fibrillation describe as the heart “racing” and “fluttering.” The condition of the heart being out of rhythm is known as arrhythmia. Atrial fibrillation (also called Afib or AF) is the most common type of heart arrhythmia.

In Afib, the atria’s erratic contractions do not allow it to pump blood effectively, and that allows blood to collect in the left atrial appendage of the heart, where blood clots can form. If a blood clot travels to the brain, stroke can occur. For that reason, it is critical to have Afib addressed by a medical team. There are several options for Afib treatment. Information about Afib, including treatment options and risk factors, is found here.