The cardiovascular system is made up of the heart, blood, and blood vessels, and is responsible for transporting nutrients, gases, and wastes to and from cells, aids in fighting disease and helping to stabilize body temperature. The process by which this is all achieved consists of systemic circulation--when oxygenated blood is pumped away from the heart to the body and returns deoxygenated blood back to the heart--and pulmonary circulation--when oxygen-depleted blood is pumped away from the heart to the lungs and returns oxygenated blood back to the heart.
The heart is responsible for pumping blood through the blood vessels by repeated, rhythmic contractions. The heart is composed of cardiac muscle, an involuntary muscle tissue which is found only within this organ. The average human heart, beating at 72 BPM, will beat approximately 2.5 billion times during a lifetime spanning 66 years.
The heart consists of four cavities called chambers, which consists of two atria and two ventricles. The right and left atria are situated on top, while the right and left ventricles are situated on the bottom. A wall, called the septum, separates the right and left sides of the heart. 
- the right atrium receives oxygen-depleted blood from the body
- the right ventricle receives oxygen-depleted blood from the right atrium and pumps it to the lungs
- the left atrium receives oxygen-rich blood from the lungs and pumps it into the left ventricle
- the left ventricle receives oxygen-rich blood from the left atrium and pumps it to the entire body
A heartbeat is defined as one complete contraction of the heart. There are several distinct stages which form a full heart beat. Cardiac Systole describes the period at which the heart contracts and Cardiac Diastole describes the period of relaxation, between beats (thus, the terms diastolic and systolic pressure, in relation to blood pressure). They can be further divided into diastole and systole of the atria and ventricles.
Blood vessels are hollow tubes that carry blood throughout the body. They consist of arteries, veins, and capillaries. Arteries carry oxygen-rich blood away from the heart. Veins carry oxygen-poor blood back to the heart. In pulmonary circulation, this is reversed. It is the pulmonary artery that brings oxygen-poor blood into the lungs and the pulmonary vein that brings oxygen-rich blood back to the heart.
Arteries branch into smaller vessels called arterioles. Arterioles further branch into capillaries, which deliver oxygen and nutrients to cells. Most capillaries are thinner than a hair. Many are so tiny, only one blood cell can move through them at a time. Once the capillaries deliver oxygen and nutrients and pick up carbon dioxide and other waste, they move the blood back through wider vessels called venules. Venules eventually join to form veins, which deliver the blood back to your heart to pick up oxygen.
Blood is the fluid which circulates through the heart, arteries, veins, and capillaries. Composed of red blood cells, white blood cells, blood platelets, and an interstitial fluid called plasma. Delivers nutrition and oxygen for tissues far from food and air supply, and transports waste from the tissues to the excretory organs. Blood also provides thermal and chemical regulation to the body and aids in preventing infection by transporting antibodies. 
Besides circulating blood, the blood vessels provide us with pulse and blood pressure. Pulse, or heart rate (the rate at which the heart beats), is measured by touching an artery. Heart Rate (HR) is expressed in beats per minute, or BPM.
The measurement of blood pressure uses the blood flowing through the arteries because it has a higher pressure than the blood in the veins. Blood pressure is measured using two numbers. The first number, which is higher, is taken when the heart beats during the systole phase (systolic pressure). The second number is taken when the heart relaxes during the diastole phase (diastolic pressure). 
Normal systolic pressure ranges from 120 millimeters of mercury (mmHg) to 130mmHg. Normal diastolic pressure ranges from 80mmHg to 85mmHg. Blood pressure may be influenced by a number of factors such as diet, medication, weight, physical activity, alcohol, smoking, stress, and the intake of various dietary supplements. Research has been shown that a diet rich in fruits and vegetables, with reduced total fat to include saturated fat and low-fat dairy products can significantly reduce hypertension (high blood pressure). Blood pressure is measured by a sphygmomanometer, or blood pressure cuff.
- ↑ various (n.d.). Circulatory System. Wikipedia. Retrieved on 2008-09-29.
- ↑ various (n.d.). Structure of the Human Heart. The Franklin Institute. Retrieved on 2008-09-29.
- ↑ various (n.d.). Respiratory Disorders Glossary. LPCH.org. Retrieved on 2008-10-01.
- ↑ 4.0 4.1 4.2 4.3 various (n.d.). The Cardiovascular System. Texas Heart Institute. Retrieved on 2008-09-29.
- ↑ Donche, Dan (2008). FF Trainer Certification Guide. USA: Fatal Fitness.
- ↑ Brookes, Douglas S. (2004). The Complete Book of Personal Training. Champaign, IL: Human Kinetics, 288-289.
- ↑ 7.0 7.1 unknown. (n.d.). Blood Vessels. The Franklin Institute. Retrieved on 2008-09-29.