The human heart is an amazing pump. The function of the heart is to circulate (pump) blood throughout the body to provide oxygen and nutrients and to remove waste products. The heart then pumps the deoxygenated blood through the lungs to release carbon dioxide and collect oxygen.
Some organs are crucially dependent on continuous and adequate oxygen supply. For instance, impaired blood flow might lead to brain damage within minutes.

The heart:

• is a muscle about the size of your fist.
• weighs approximately one pound.
• is located behind and slightly to the left of the breastbone
• pumps about 5 liters of blood every minute, or 7000 liters of blood every day.

The pumping ability of the heart is controlled by an internal electrical system. Problems with the heart's electrical system can cause heart rhythm disorders, such as ventricular tachycardia, that may lead to sudden cardiac arrest (SCA).

The heart's electrical system controls the synchronised and rhythmic pumping efficiency of the heart. It

controls the heart rate (the number of beats perminute). cas a special circuit (conduction pathway) that carries electrical signals throughout the upper heart chambers (atria) and the lower heart chambers (ventricles) for each heartbeat.

When heart cells in the upper heart chambers (atria) receive an electrical signal, they contract (pump) and then relax. The blood from the atria is pumped into the relaxed lower heart chambers (ventricles). The ventricles then pump blood to the body.

Electrical Path within the Heart
In a healthy heart, each heartbeat begins in the sinus node (the heart's natural pacemaker), which is located in the right atrium. The electrical signal from the sinus node (sinoatrial or SA node) starts an electrical chain reaction that spreads across both atria. This causes the atria to contract and pump blood into the ventricles.
This electrical chain reaction continues from the atria through an area between the atria and ventricles called the atrioventricular (AV node or AV) junction. The AV node connects to conduction pathways that relay the signal to both ventricles. The AV node acts as an electrical gateway to the ventricles. The conduction pathways deliver the signals to the ventricles, and the ventricles contract and pump blood to the body.
An irregularity in the heart's electrical system is called an arrhythmia, or heart rhythm disorder. Rhythm disorders can cause the heart to beat too slowly (bradycardia), too fast (tachycardia), or not in sequence (asynchrony). An arrhythmia can compromise the heart's ability to pump and circulate blood through the body and brain.

The Heart's Function

A healthy heart is very sensitive to the body's needs. It adjusts its rate of pumping blood to match the body's need for oxygen and nutrients. An average person has approximately 120,000 heartbeats a day

A normal heart rate can range from 60-140 beats per minute depending upon age and whether the person is at rest or exercising. The younger the person, the faster the heart rate. As you exercise or perform daily activities, your heart increases its rate to ensure that it is supplying enough oxygen to your muscles to meet the needs of the activity. In a matter of seconds, the heart can increase its pumping volume up to four times the amount that it pumps when at rest.

The pumping efficiencyof the heart is evaluated using a measurement called ejection fraction (EF). The ejection fraction of the heart is defined as the fraction or proportion of blood that the heart pumps (or ejects) out of the left ventricular chamber with each heart beat. People with a normal, healthy heart have an EF of 55 percent or greater. This means that 55 percent of the blood that fills the left ventricle is pumped out to the body with each contraction.

A low ejection fraction is one of the key indicators used to identify people who are at risk for sudden cardiac arrest. Many people with heart disease can have an EF of 40 percent or less. A below-normal EF means your heart is no longer pumping efficiently and therefore may not be able to supply your organs and the rest of your body with enough blood. If your EF is abnormally low, you may need further tests to determine if you are at risk for abnormal heart rhythms.

The Heart's Structure

The heart has four chambers: Two smaller, upper chambers (the right and left atria) Two larger, lower pumping chambers (the right and left ventricles)
The upper and lower chambers are separated by walls of non-conducting tissue, which contain one-way valves to allow blood to flow between them. These heart valves also ensure the forward motion of blood. The heart is separated into right and left sides, with each side performing a unique function:
The right side of the heart receives deoxygenated blood from the body and sends it to the lungs to pick up oxygen. The left side of the heart receives oxygenated blood from the lungs and sends it to the rest of the body where the oxygen is delivered to organs such as the brain and kidneys.

Last Updated on: 20.01.2005