Chest burn and Fainting. Approach.

Recently my father has been diagnosed with HPylori infection. In the month of October when he fainted first Doctor performed ECG and he found minute difference in the graph and asked to get admitted in Godrej hospital. At Godrej hospital they performed ECG and it was normal. They also performed Angiography and found 80% blockage in internal vain. The doctor suggested that it may not cause any issue and change in lifestyle can help you improve the situation. He was discharged in 2 days. Post that as he was still facing similar issue and on doctors advice an endoscopy was conducted where HPylori infection was identified. The Doctor gave 14 days HP kit. After 14 days HP kit he was asked to take regular medicines. Now after 17 days of the course he felt the same and fainted. What could be the cause of the same and to which specialist we should approach.