Below is an instruction from Human. Write a response.
    ### Instruction:
    What causes Angina ?
    ### Response:
    Underlying Causes
                
Angina usually is a symptom of coronary heart disease (CHD). This means that the underlying causes of angina generally are the same as the underlying causes of CHD.
                
Research suggests that CHD starts when certain factors damage the inner layers of the coronary arteries.
    