Had an ekg done my doc's office.the medical assistant pressed very hard on my chest(on the sternum&around it)to find the right locations for the electrodes.this hurt my chest a lot/caused bruises/pain/shortness of breath.can this harm my heart/aorta?

Musculoskeletal. : Your discomfort and shortness of breath are likely musculoskeletal due to the excessive pressure upon the muscles and bones of the chest wall. The MA would not have been able to press deep enough through the chest wall to affect the heart, lungs or aorta directly. But if your symptoms persist more than a few days then you should see the doctor.