The Heart, Unsurprisingly, is a really powerful muscle in the body as well as being the most important. As most are aware blood from the heart and the lungs is pumped through arteries, capillaries and veins, which in turn pump it back to the heart and the lungs.
Oxygen nourishes the cells as it is carried in the blood as it circulates the body. You need a healthy supply of Oxygen to stay healthy. If blood circulation is restricted or reduced, so is the amount of oxygen that reaches the body. This can then cause any number of cardiovascular diseases.
Smoking and atherosclerosis (This is the progressive thickening and hardening of the arteries). Over a period of time in your life span fatty deposits, like cholesterol, build up in the arteries, reducing the size of the area that the blood can pass through. This restriction obviously disrupts the flow to important organs like the heart and the brain. Atherosclerosis is the main cause of strokes, heart attacks, and most Cardiovascular diseases. Smoking speeds up the processes as the tobacco smoke accelerates the build up of plaque and cholesterol.