Final answer:
Atherosclerosis is the most common cause of ischemic heart disease, as it leads to the build-up of plaque in the coronary arteries, reducing blood flow to the heart muscle.
Step-by-step explanation:
The most common etiology for ischemic heart disease is atherosclerosis, which is the build-up of plaque in the arteries of the heart (coronary arteries). Atherosclerosis involves the accumulation of fatty material, including cholesterol and white blood cells, within the walls of the arteries, which obstructs blood flow and decreases vessel flexibility.