I've been taking lessons with a temporary coach that likes to do intense, non-stop drilling. Literally 15 straight minutes of forehands and backhands in a 5 ball sequence. Of course, my heart is absolutely pounding, but weird thing is I don't feel muscle fatigue. My legs and arms don't burn, but my heart's about to jump out of my chest. Is it normal that I only feel the effects in my heart because whenever I do intense cardio (insanity), I definitely feel the burn?