Smoking

Smoking is widely regarded as the single biggest risk factor for cardiovascular disease.

Smokers face approximately thrice the risk of having heart attacks than non-smokers. They are also more than twice as likely to meet with sudden cardiac death. The same health risks apply to passive smokers, i.e. people who do not themselves smoke but who are nonetheless constantly exposed to smoke exhaled by others in their proximity.
Smoking is a major cardiovascular risk factor because of the poisonous effects of the chemicals contained in tobacco. For instance, nicotine causes a rise in blood pressure, narrowing of the blood vessels, irregular heartbeats and spasms of the muscles in arterial walls. Similarly, the carbon monoxide in cigarette smoke damages the inner lining of the blood vessels as well as reduces the oxygen level in blood. This irritates the blood vessel walls and may trigger the onset of atherosclerosis.
Quitting smoking, or refraining from the first puff, will contribute significantly to the prevention of heart disease, as well as arrest the deterioration of any existing heart conditions.