I've had this happen. FAA ordered me to see a cardiologist. Had to do blood work, holter monitor for 24 hours, nuclear stress test with treadmill and the whole shebang, and another ECG. They let me keep my medical while I was being evaluated. It took about 4 months and 4000 dollars out of my pocket since the cardiologist and the insurance company agreed that these test were completely unnecessary. I was 35 years old. Not a smoker. In good shape. No history of cardiac issues. In the end they said I was in great health and I could keep my medical. I stay away from caffeine before my medicals now and I haven't had any issues since. Very stressful time though.