My boyfriend woke up and his chest is hurting on the middle left side what can be the cause?

Chest pain: Chest pain has many causes. At a young age, cardiac (heart) is usually less likely, but still needs to be ruled out. With chest pain, L sided, have him call his Dr. ASAP r get evaluated ASAP to assure it is not his heart, than work on different causes if /once that is ruled out. Best wishes.

Lots of differential: Anything as minor as heart burn or acid reflux to as serious as angina,