Your heart is a muscle. Its job is to pump blood around your body.
- It is about the size of your fist.
- It is protected by your ribs and breastbone (sternum).
- It beats about 100,000 times a day.
Each beat of your heart pumps blood through a network of arteries and veins.
- Blood delivers essential oxygen and nutrients to every cell.
- Blood takes away waste products and carbon dioxide.
- Arteries carry oxygen-rich blood from the heart throughout the body.
- Veins carry oxygen-poor blood back to your heart and lungs to start the cycle over again.
Like any other muscle, the heart needs its own supply of oxygen-rich blood to function. The coronary arteries handle this job. Coronary artery disease is when the coronary arteries become narrowed or blocked so your heart does not get enough oxygen to do its job effectively.
Anatomy of the heart
Your heart is divided into four sections or chambers. The two chambers on the top are called atria and the two chambers on the bottom are called ventricles.
A muscular wall called the septum separates the right side of the heart from the left.
On the right side of the heart, there is a right atrium and a right ventricle. The right side receives oxygen-poor blood from the rest of the body.
On the left side of the heart, there is a left atrium and a left ventricle. The left side receives oxygen-rich blood from the lungs.
The four chambers are separated by one-way valves that open and close with every heartbeat. There are four heart valves.
- Aortic valve
- Tricuspid valve
- Pulmonary valve
- Mitral valve
These one-way valves keep the blood flowing in one direction through the different chambers of the heart and out to the body. The heart “beats” that your doctor hears with their stethoscope is the sound of your valves opening and closing to let blood through.
Valves that don’t work properly can lead to different types of valvular heart disease. For example, If a valve doesn’t close correctly, blood may leak between the chambers or flow backwards (valve regurgitation, insufficiency or incompetence). If a valve becomes narrowed (valve stenosis), blood flow through the heart may be restricted. Valves can be damaged by infection (endocarditis), rheumatic heart disease, congenital heart defect, normal aging and wear.
How your heart works
To pump blood throughout the body, your heart contracts then relaxes. This action is similar to clenching and unclenching your fist. With each beat of your heart, blood is pushed through your arteries. This is what creates your pulse.
- The right atrium is full of oxygen-poor blood from your body (muscles, organs, brain and heart). When the right atrium becomes full, it contracts. When the atrium contracts, the tricuspid valve between the right atrium and the right ventricle opens. The blood flows into the right ventricle.
- When the right ventricle is full it contracts and pumps the blood to the lungs through the pulmonary valve
- In the lungs, carbon dioxide is removed and fresh oxygen is added to the blood. The blood is now oxygen-rich. Oxygen-rich blood then flows into the left atrium.
- When the left atrium contracts, the mitral valve between the left atrium and left ventricle opens. The blood flows into the left ventricle.
- The left ventricle pumps the oxygen-rich blood into the aorta through the aortic valve and out to the rest of your body.
- The oxygen-rich blood travels throughout your body. Veins carry the oxygen-poor body back to the right atrium. The right atrium fills with oxygen-poor blood. The cycle begins again.
Your heart rate is the number of times your heart beats per minute. Normal heart rate varies from person to person, but a normal adult resting heart rate is usually about 60 to 100 beats per minute. During rest, your heartbeat will slow down. With exercise, it will beat faster. Knowing your heart rate can help you spot health problems.
There is an electrical system inside your heart that controls the rate (speed) and rhythm of your heart. A normal heart rhythm is called normal sinus rhythm (NSR).
When there is a problem with your heart rhythm or rate, it is called arrhythmia.
The heart’s electrical system
An electrical system in the heart makes sure the heart beats in a regular rhythm and normal rate. It starts with an electrical signal in the right atrium, at the SA Node (sinoatrial node). The electrical signal then spreads throughout the heart from top to bottom (from atria to ventricles). As one part contracts, the others relax in a sequence.
- The electrical signal travels from the SA node to the atria causing them to contract pumping blood into the ventricles.
- Then it goes to the AV node (atrioventricular node) between the atria and the ventricles. The signal is held there for a moment while the blood is being pumped into the ventricles.
- Then the signal moves to the ventricles through fibres inside the septum and ventricle walls called “bundle of His” and “Purkinje fibres”. This makes the ventricles contract – sending blood to the lungs and to the rest of your body.
An electrocardiogram (ECG or EKG) is a test that helps to diagnose a problem with your heart's electrical system. It measures electrical signals as line tracings on paper.