Presumably the CK was done to evaluate for a cardiac cause of the heartburn symptoms. Now that the CK came back positive, I think his doc is obligated to fully evaluate for a cardiac cause of his symptoms - EKG, CK isoenzymes, troponin I, CXR, possibly a stress test. Incidentally, cardiac ischemia can result in an elevated AST.
I personally wouldn't get a CK in a person with reflux symptoms (though I might do an EKG), but now that its been done, his doctor needs to follow up on it.
CK isoenzymes would be especially helpful in this case- although not very sensitive/specific, would help in the evaluation of a cardiac vs muscle cause.