Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Electrocardiogram ?
    ### Response:
    An electrocardiogram (e-lek-tro-KAR-de-o-gram), also called an EKG or ECG, is a simple, painless test that records the heart's electrical activity. To understand this test, it helps to understand how the heart works.
                
With each heartbeat, an electrical signal spreads from the top of the heart to the bottom.
    