Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Heartburn ?
    ### Response:
    Heartburn is a painful burning feeling in your chest or throat. It happens when stomach acid backs up into your esophagus, the tube that carries food from your mouth to your stomach.    If you have heartburn more than twice a week, you may have GERD. But you can have GERD without having heartburn.
    