My son, 14 years old, 6'2", 195 pounds, size 17 shoes.... big boy.... Started last month noticing his heart "beating really hard" and getting out of breath during exercise. He's in great shape, competitive basketball player, but seems to get winded and feels his heart beating with moderate activity. We have seen an electrophysiologist, had an EKG, an echo cardiogram, and stress test. ALL came back normal. No irregular beats. Just yesterday, he noticed a tingling in his arms during exercise..... What could all of this be?