I am an active 80 year old female. I am in the process of all kinds of tests to determine what is going on with me...Heart monitor, PET scan, MRI on my lungs, Echocardia. When I wore a heart monito, I was only told by my doctor that my heart is beating too fast...put me on Metrolpolol 25 mg. My doctor is a DO -- not an MD. He seems to be doing everything he can to determine why I still have this fuzzy head though I am on oxigen at night. My latest test is for an overnight sleep apnea test. At what point should I move onto a Cardiologist?