These letters stand for "Electrocardiogram".  It is also called EKG. 

      This is a simple test to check your heart rhythm and other abnormalities that might determine if other tests are needed to evaluated chest pains, fatigue, shortness of breath and fainting among other symptoms.  It is easily done by sticking some gel pads to your chest attached to a special computer that does the analysis of the electrical waves in your heart muscle.