The nicotine raises blood pressure, which is a risk factor in itself, smoking also causes damage to the lining of arteries which increases the likelihood of fatty plaques forming. It also decreases levels of high density lipoprotein (HDL), which removes fat from the lining of arteries. If a fatty plaque completely blocks one of your coronary arteries that causes a heart attack. Smoking also increases the tendency of blood to clot, so its possible that blood clots can form near the plaques and make a heart attack even more likely. Damage to your lungs also makes exercise more difficult, which would otherwise help prevent heart disease.