Yes An electrocardiogram (ECG or EKG) can detect a blockage in your heart.
Some signs that you may have a blockage in the arteries or blockage in your heart are shortness of breath or extreme fatigue following exercise or physical stress.
A blockage of the heart or arteries can lead to a heart attack if not corrected so if you think you may have a blockage of your arteries or a blockage of the heart the EKG can detect whether or not you have blocked arteries or blockage of the heart.