Heart attacks generally result from the condition called coronary heart disease or CHD (C-H-D). Therefore, both primary and secondary risk factors that promote CHD may also increase the risk of a heart attack. Primary factors are those shown by research to be closely linked to an increase in risk of heart and blood vessel disease. Secondary or contributing factors are those often associated with such disease, but about which the significance hasn't been determined. The primary risk factors for a heart attack are usually considered to be increasing age, belonging to the male gender, and heredity. For example, men between the ages of 35 and 65 are generally more likely to experience fatal heart attacks than women in the same age range. The risk seems to increase for women after the age of menopause, however. Hereditary considerations include both race and parental health: African Americans are at higher risk of heart disease, as are children whose parents have a heart condition. Secondary or contributing risk factors for heart disease include cigarette smoking, uncontrolled high blood pressure, obesity, high blood cholesterol levels, and lack of daily aerobic exercise. While each of these risk factors can be a concern individually, a combination of two or more is thought to increase risk substantially. For example, cigarette smoking can more than double the likelihood of fatal heart attack as well as other heart diseases. High blood pressure can force the heart to work harder, resulting in enlargement, weakening, and eventual failure. Weighing 30 percent more than the ideal for a given height and build may put significant excess strain on the heart, possibly leading to heart failure. Worse, obesity often adversely affects blood pressure, cholesterol levels, and activity levels, compounding the risk for coronary heart disease. High blood cholesterol may also introduce a long list of related risk factors: excess plaque build up within arterial walls, narrowing and hardening of those walls, decreased pumping efficiency of the heart, enlargement and weakening of the heart, and eventual heart failure. Finally, a sedentary lifestyle may also be linked to heart disease because it allows the heart muscle to become de-conditioned, promotes obesity and the related heart disease risk factors, and can make it more difficult to control both high blood pressure and high cholesterol.