This Section is designed to help you understand your heart and its various parts and components that need to be operating in unison for it to be functioning appropriately.

Understanding your heart and the various diseases associated with it should start with understanding your healthy heart. In following tutorial we can take you through the various components that make the heart function normally.

There are 4 large components of the heart: 1. The heart muscle 2. The valves of the heart, 3. The blood supply to the heart, 4. The electrical system of the heart. If any of these four components go wrong it can affect how your heart functions.

THE HEART:

The hollow center of your heart is divided into four sections, called chambers. Each chamber is like a separate room, with doors (valves) that let blood in and out.

Where Blood Flows In — The Atria

The two upper chambers in your heart are called the atria. The atria are the receiving chambers of your heart. When blood flows into your heart from the body or lungs, it always flows into either the right or left atrium — never anywhere else. (One upper chamber is called an atrium. Both upper chambers together are called the atria.) Blood from the body goes to the right atrium, while the left atrium receives blood from the lungs, through structures called the pulmonary veins.

Where Blood Is Pumped Out — The Ventricles

The two lower chambers in your heart are called ventricles (Figure 1). The ventricles are the pumping chambers of your heart. When blood leaves your heart, it is always pumped out from the ventricles — never from anywhere else. The ventricles are very strong because they have to pump hard enough to push blood through your lungs and entire body.

Your Heart's Right and Left Sides

Sometimes the right and left sides of your heart are called your right heart and left heart. The right atrium and right ventricle are, of course, on the right side of your heart (the same side as your right arm), and the left atrium and left ventricle are on the left side of your heart.
A wall, called the septum, separates the left and right sides of your heart. Blood that hasn't yet been to the lungs (blood with no oxygen) stays on the right side of the septum. Blood returning from the lungs (blood with oxygen) stays on the left side of the septum.

What Do Your Valves Do?

Your heart valves keep blood flowing in one direction through your heart, just like the one-way valves in your home's plumbing. They open to let blood flow through, and then close to prevent blood from flowing back the way it came. When a valve closes, flaps of tissue on the valve close tightly together to create a seal. These flaps of tissue are called leaflets.

Where Are Your Heart Valves?

Your heart has four valves. Blood flows through each valve one time on its way through your heart. The four valves can be grouped by their job:

• Atrioventricular — Atrioventricular valves control blood flow between your heart's upper and lower chambers. The valve between the right atrium and the right ventricle is called the tricuspid valve. The valve between the left atrium and the left ventricle is called the mitral valve.
• Semilunar — Semilunar valves control blood flow out of your heart. Blood flows out of the right ventricle to the lungs through the pulmonary valve. Blood flows out of the left ventricle to your body through the aortic valve.

FOLLOWING THE BLOOD TRAIL:

If we follow the blood through the heart and see how the valves and heart muscle function together over one beat it would beat like this:

1. The non-oxygenated blood returns from the vitals organs and muscles to the right atrium.
2. The right atrium then passes the blood through the tricuspid valve (valve that separates the right atrium from the right ventricle) into the right ventricle.
3. The right ventricle then passes the blood pass the pulmonic valve into the pulmonic artery and lungs. The blood will pick up oxygen from the lungs.
4. After obtaining the oxygen from the lungs, the blood enters into the pulmonary veins. The pulmonary veins bring the blood back to the left atrium.
5. The left atrium then pumps the blood pass the mitral valve into the left ventricle.
6. The left ventricle is the main pumping chamber of the heart. After receiving the blood from the left atrium, the left ventricle then pushes the blood pass the aortic valve into the aorta. The Aorta is the main artery in the body. This then delivers the blood to the muscles and vital organs.

What Makes Blood Flow?

Blood doesn't flow by itself — your heart's chambers work hard to keep blood moving. The chambers relax and expand to let blood flow into them. Then they tighten and pull inward (contract) to help push blood out.

You might hear your nurse talk about your diastolic pressure or systolic pressure when you get your blood pressure checked. When a chamber is relaxed, or expanded, it is in diastole. When a chamber is contracted, or small, it is in systole.

Your Heart's Electrical System

What Is the Electrical System in Your Heart?

The electrical system in your heart controls the speed of your heartbeat. The system includes a network of electrical pathways, similar to the electrical wiring in your home. The pathways carry electrical signals through your heart. The movement of the signals is what makes your heart beat.

When working properly, your heart's electrical system automatically responds to your body's changing need for oxygen. It speeds up your heart rate as you climb stairs, for example, and slows it down when you sleep. When your heart rate speeds up, it means your heart pumps faster and your body gets more oxygen-rich blood.

Your heart's electrical system is also called the cardiac conduction system.

Parts of the Electrical System

Your heart's electrical system includes three important parts (Figure 1 above):

• S-A node (sinoatrial node)
• A-V node (atrioventricular node)
• His-Purkinje system

The S-A Node: Your Heart's Natural Pacemaker

The S-A node is a bundle of specialized cells in your right atrium. The S-A node cells are special because they create the electricity that makes your heart beat. The S-A node normally produces 60-100 electrical signals per minute — this is your heart rate, or pulse.

The S-A node is called the "natural pacemaker" of your heart because it controls your heart rate.

The A-V Node: Your Heart's Electrical Bridge

The A-V node is a bundle of specialized cells between your heart's upper and lower chambers (between the atria and ventricles). The A-V node cells are special because they allow electricity to pass through them. Except in rare conditions, no other cells between the atria and ventricles allow this. So, the A-V node is the "electrical bridge" between the atria and ventricles.

Some types of slow heart rhythms (bradycardias) are caused by problems in the A-V node.

The His-Purkinje System

The His-Purkinje system is in your heart's ventricles. Electricity travels through the His-Purkinje system to make your ventricles contract. The parts of the His-Purkinje system include:

• His Bundle (the start of the system)
• Right bundle branch
• Left bundle branch

Purkinje fibers (the end of the system)

CONDUCTION SYSTEM AND BLOOD FLOW

Electrical signals created by the S-A node follow a natural electrical pathway through your heart walls. The movement of the electrical signals causes your heart's chambers to contract and relax. When a signal passes through a chamber wall, the chamber contracts. When the signal has moved out of the wall, the chamber relaxes. In a healthy heart, the chambers contract and relax in a coordinated way, or in rhythm.

When your heart beats in rhythm at a normal rate, it's called sinus rhythm. A problem in your heart's electrical system can disrupt your heart's normal rhythm. Any kind of abnormal rhythm or heart rate is called an arrhythmia. It's normal and healthy for your heartbeat to speed up or slow down during the day as your activity level changes. But it's not normal for your heart to beat out of rhythm. When your heart beats out of rhythm, it may not deliver enough blood to your body.

The Path of an Electrical Signal

	STEP 1. The S-A node (natural pacemaker) creates an electrical signal.
	STEP 2. The electrical signal follows natural electrical pathways through both atria. The movement of electricity causes the atria to contract, which helps push blood into the ventricles.
	STEP 3. The electrical signal reaches the A-V node. There, the signal pauses to give the ventricles time to fill with blood.
	STEP 4. The electrical signal spreads through the His-Purkinje system. The movement of electricity causes the ventricles to contract and push blood out to your lungs and body.

A snap shot of the heart's electrical activity can be captured on an electrocardiogram. Please review the other sections for more information regarding specific conditions.