Hello welcome to HCM. Atherosclerotic heart disease is a multifactorial disease affected by genetic and environmental factors. The risk factors for atherosclerotic heart disease are strong family history, obesity, smoking, male sex, blood ptessure, diabetes, age, improper diet and many others. A combination of these factors lead to deposition of cholesterol in the walls of the heart vessels causing them to narrow. Narrowing of the artery decreases blood supply to the heart and hence the patient gets chest pain. Narrowing of the arteries critically also leads to stagnation of blood cells called platelets causing clot formation which you are referring here to dried up blood. This can lead to a heart attack. A bypass surgery uses alternative grafts to bypass the blocks so that the blood of supply to the heart is restored. I hope I have answered your query satisfactorily. Wishing you good health regards