Q: Given a scientific passage and an answer, generate a question for the given answer.
Passage: If plaque blocks coronary arteries that supply blood to the heart, coronary heart disease results. Poor blood flow to the heart may cause chest pain or a heart attack. A heart attack occurs when the blood supply to part of the heart muscle is completely blocked so that cardiac muscle cells die. Coronary heart disease is the leading cause of death in U. S adults. Answer: plaque
A:
Coronary heart disease is caused when what blocks coronary arteries?