The Normal Heart

Heart Structure
The heart has four chambers arranged roughly in a square (see diagram). The upper chambers are called the atria (right and left) and the lower chambers are called the ventricles (right and left). Each atrium communicates with the ventricle below by a one-way valve. On the left side of the heart, this valve between the left atrium and left ventricle is called the mitral valve. On the right side of the heart, the valve between the right atrium and right ventricle is called the tricuspid valve. These valves are made of collagen and connective tissue and consist of several leaflets that come together to form a tight seal when the valve is closed. Normal valve leaflets are very smooth with straight edges, like a door.

The large blood vessel leading from the right side of the heart to the lungs is called the pulmonary artery. A one-way valve connects the pulmonary artery to the right ventricle. This is called the pulmonary valve.
The large blood vessel leading from the left side of the heart to the rest of the body is called the aorta. A one-way valve connects the aorta to the left ventricle. This is called the aortic valve.

What is the Heart’s Job?
The right side of the heart receives poorly oxygenated blood from the body and pumps it to the lungs, where the blood absorbs oxygen. Next, the blood returns to the heart (left atrium) and is pumped by the left ventricle to the rest of the body. After delivering oxygen and other nutrients to the rest of the body, blood returns to the right heart.  This cycle continues with each heartbeat.

What Happens During a Heartbeat?
Blood returning from the lungs fills the left atrium and blood returning from the rest of the body fills the right atrium. The ventricles, after having ejected their content into the two arteries (aorta and pulmonary artery) relax, and blood is allowed to flow from the atria to the corresponding ventricle (this phase of the heart cycle is called diastole). This one-way direction of blood flow is controlled by the mitral and tricuspid valves. Next, the heart muscle contracts and the ventricles pump the blood out to the lungs and the rest of the body. During this part of the heartbeat, the mitral and tricuspid valves are tightly closed, to keep the blood flowing in a forward way. This forces the blood to travel through the pulmonary and aorta arteries (this phase is called systole), which are the biggest vessels leading from the heart to the rest of the body. This one-way direction of blood flow is controlled by the pulmonic and aortic valves.

 

HEART DRAWING OF A DOG