The cardiovascular system includes not only the heart, but also the living blood vessels that include arteries and capillaries that carry blood through the body. Blood shuttles oxygen from the lungs, food for our tissues, hormones (or chemical signals), and a host of other cells with specific roles and functions. The definitions that follow identify the components of this elaborate operation.

Heart This organ provides the driving force of the entire system. It rhythmically contracts at a self-generated pace, although heart rate can be modified by numerous external effects. The contractions propel blood through the vascular system to allow delivery of oxygen, carbon dioxide, and food to individual tissues. More on the heart

Vascular System
A closed circuit of branching blood vessels that carries and transfers blood products to organs and tissues. It is composed of three primary forms:

Arteries
Branching, elastic tubes that carry blood AWAY from the heart. The blood contained within them is usually oxygen-rich and under high fluid pressure. The primary exception to this rule are the pulmonary arteries, which carry oxygen-poor blood from the heart to the lungs.

Veins
Thinner walled branching vessels that carry low fluid pressure blood (generally oxygen-poor) back to the heart. The only veins that carry oxygen-rich blood are those that return blood from the lungs to the heart.

Capillaries
Tiny intermediate vessels between arteries and veins where gas and food exchange occurs within individual tissues. In order to reach the many cells of tissues that depend on the vascular system as a supply line, capillaries split into elaborate branching networks of interconnecting, microscopic vessels.

Circulation 

Blood
The fluid that travels in the vascular system. Blood is actually a mixture of components:

• Plasma - a fluid substance which is mostly water, salts and protein
• Red Blood Cells (RBC) - cells that give blood its characteristic red color and ability to transport oxygen
• White Blood Cells that mediate inflammation(for example, in response to infection).

Two sac-like organs that occupy the chest cavity and uptake air from the surroundings. They contain large numbers of tiny, specialized air sacs that collect air into blind tunnels where blood in capillaries can intermingle with them and engage in gas exchange. More on the lungs

Neuroendocrine System
This system coordinates different functions of the body. It is primarily composed of the interaction of the nervous system and organs that produce hormones. In part, this system regulates effects to the heart and vascular system.

Controlling the heart 

Heart Failure can follow immediately after a problem or injury affects the heart, but more commonly it develops months or years later. Once initiated, the cardiovascular system may be unable to carry out it's functions properly. Compensatory changes may be desirable or deleterious. In general, heart failure is a progressive disorder which can begin with any number of culprits and deteriorate if left untreated.