There can be many diseases that can lead to the symptoms. I would assume that the cardiologist has already evaluated him via a stress echocardiogram and event/Holter monitor. A carotid ultrasound looking for stenosis can also be considered.
Regarding GI causes, an upper endoscopy can be considered to look for upper GI diseases - such as GERD, inflammation or an ulcer.
At this time, a neurology referral can be considered. A brain MRI can look for intracerebral causes of dizziness.
This option can be discussed with his personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
kevinmd_