How is heart disease caused?

Many causes. Heart disease can be caused by many things such as genetics or a bacterial infection. Perhaps the most common risk factors are related to lifestyle and thus can be changed. Smoking, excessive alcohol use, obesity, or uncontrolled blood sugars in a diabetic are all important risk factors for cardiovascular disease.
Many causes. Congenital (born with it), degenerative (old people), infection, tumor, trauma, drugs (licit and illicit), radiation, diabetes, smoking, excessive alcohol (see drugs), and many rare causes. But the 2 biggest causes are: high blood pressure and hardening of the arteries (atherosclerosis).