Why Would Chest Pain Occur After Having Been Treated With Angioplasty?

My father had a heart attack in 2001.he was treated with an angioplasty and stenting in two arteries. In 2004,he was again treated after he complained of chest pain and angioplasty was done in the third artery. Since then he has been enjoying good health ,by God;s grace.We have been visiting for check ups and other local clinics periodically,and all the tests have been satisfactory. He has been very active in his work,walking,exercising,etc.as per your recommendation. Last to last week too he got all the medical tests done like,cholesterol,bp,ecg.etc and all the test were satisfactory. Last week on a trip ,he complained of pain in his left arm and chest. He was immediately admitted to hospital.The doctors kept him on medication and observation for two days.The Torq- blood test showed negative results,and thus ruled out any evidence of heart attack.He was released with an advice to get a detailed check up done,in some time. We recently visited a senior cardiologist in , who advised us to get an eco and ecg test done.Thankfully, both the tests showed satisfactory reports.The doctor then suggested to go for angiogram. We consulted yet another senior cardiologist from anothyer hospital and he suggested to first go for Sterss Thalium test. We are actually confused now to decide the next course of action because of two different opinions from senior cardiologists. My father just retired from his firm and is doing well now and does not seem to have any problem,by Gods grace.He has started his morning walk and is feeling absolutely fine.