anemia

A shortage of hemoglobin in the blood, reducing the ability of the blood to deliver oxygen and remove carbon dioxide throughout the body.

aorta

The large artery which sends fresh, oxygenated blood out to the body.

arterioles

The thinnest arteries, they connect the larger vessels with the capillaries.

artery

The vessels that carry blood away from the heart and into the body. These are the largest vessels and have thick, strong, elastic walls that can handle the powerful rush of blood as it is pumped out of the heart. The arteries are typically positioned far inside the body for protection.

atrium

One of two upper chambers of the heart. There is a right atrium and left atrium. Plural: atria. These chambers receive the used blood from the body through the veins.

blood

The blood is mostly composed of plasma. Three other components also go into blood:

Red blood cells, white blood cells and platelets

capillaries

The smallest blood vessels, finer than a human hair, that connect the arteries with the veins. Because they are so narrow, the cells of the blood must line up single file to pass through, slowing down the flow of blood. The capillary walls are also extremely thin, allowing for filtering of nutrients and waste products. No cell in the body is more than a hair's width away from a capillary.

cardiac cycle

The period from the beginning of one heartbeat to the next. It consists of contraction and relaxation. In an adult, the cycle lasts about .8 seconds.

cardiac output

A measure of the heart's ability to pump out blood.

chambers

The divisions of the heart. There are four chambers, or spaces, in the heart: the two top sections are called atria, and the two lower sections are called ventricles.

circulatory system

The circular (meaning to move in a circle) system by which the heart distributes blood throughout the body, depositing oxygen and removing carbon dioxide.

The left ventricle sends fresh oxygenated blood out to the body. It returns through the right atrium, and from there, flows to the right ventricle. The blood is pumped out to the lungs, where the it is refreshed with oxygen, and then returned again to the heart through the left atrium. The cycle is completed when the blood travels to the left ventricle to be pumped through the body again.

contracting

The action whereby the chambers in the heart become smaller (contract), thus forcing blood out (pumping). It is complemented by relaxation. Also called systole.

diastole

The period in the heart cycle where the heart relaxes, dilating (enlarging) and filling up with blood.

echocardiogram

A painless test utilizing ultrasound waves to measure the heart's ability to pump, whether any of the heart vales are malfunctioning, and/or parts of the wall of the heart that are not pumping correctly.

edema

Fluid accumulation in the tissues beneath the skin.

ejection fraction

A measure of the heart's ability to allow blood to flow back in.

heartbeat

The process of the heart's contracting and relaxing. Can be measured by the pulse.

hemoglobin

The substance found in red blood cells that gives them their color. It enables the red blood cells to carry oxygen to and carbon dioxide from cells in the body. A low hemoglobin count (less than 12 grams per 100 mililiters of blood) indicates anemia.

hypotension

Low blood pressure.

murmur

The sound the heart makes when there is some leakage between its chambers.

myocardium

The heart muscle.

pacemaker

The body's internal mechanism for regulating the pace at which the heart beats.

This part of the heart sends tiny electrical shocks to start the muscle contractions that are part of the heart's constant pumping action.

Artificial pacemakers are used when the body's own system does not operate correctly.

platelets

Small, oval cells in the blood, platelets work with plasma to stop bleeding.

pulmonary artery

The blood vessel leading from the right ventricle of the heart to the lungs.

pulmonary veins

The veins that drain the lungs and return the blood to the left atrium of the heart. There are four pulmonary veins.

pulse

The reflection of the heartbeat felt throughout the body at pulse points.

pulse points

Specific spots where the arteries are closer to the outside of the body, allowing the pulse to be felt The points are inside each wrist, inside each upper arm, on the neck, and on both sides of the groin and in the feet.

red blood cells

carry oxygen throughout the body. They are colored by hemoglobin and are shaped like oval donuts with solid centers.

relaxation

The state of the heart cycle when the chambers dilate (enlarge) and blood flows back in after contracting. Also called diastole.

septum

The muscular wall separating the four chambers of the heart.

sphygmomanometer

An instrument used to determine blood pressure.

stenosis

narrowing

stethoscope

An instrument used to hear a person's heartbeat.

systole

Contraction of the chambers of the heart. When the chambers contract, becoming smaller, blood is forced -- pumped -- out.

transducer

A small device, like a microphone, which sends and receives ultrasound waves that bounce off and echo back from the heart. It is used in echocardiograms.

valve

A membranous structure in the vein that temporarily closes to permit the flow of blood in a forward direction only.

veins

The blood vessel that return blood to the heart and lungs. They look like blue lines under the skin. Special valves prevent the blood from going in any direction but towards the heart.

vena cava

One of the body's two largest veins, they lead directly to the right ventricle of the heart.

venules

The smallest and narrowest of the veins, they connect the capillaries with the larger veins.

vessels

The tubes that carry blood through the body.

There are three kinds of vessels: capillaries,  veins and arteries.

white blood cells

Cells in the blood that fight disease. They are irregularly shaped and move slowly in the blood stream.