My 16 Year Old Son Showed Me The Left Side

my 16 year old son showed me the left side of his chest and it looks as if that side of his chest is lower than the right side. i noticed this a couple of years ago but it wasn't as bad. it has gotten worse over time and is starting to concern me more. if you look at his chest you can actually see his heartbeat right through it. is this a serious thing that i should get him checked out for.