Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Peripheral Arterial Disease ?
    ### Response:
    Peripheral arterial disease (PAD) happens when there is a narrowing of the blood vessels outside of your heart. The cause of PAD is atherosclerosis. This happens when plaque builds up on the walls of the arteries that supply blood to the arms and legs. Plaque is a substance made up of fat and cholesterol.
    