hi if stress test & ecg are normal, there is no point to worry. check out with the electrolyte levels, complete blood picture with auscultation for any ronchi or wheeze. echo as early as possible will indicate the status of the graft as well as the regional wall abnornmalities some times broncho-dilators can also cause these sort of problems. he requires a good counselling & mental support to lead good quality of life post operatively avoid excessive hard work or strenuous exercises which can cause shortness of breath all the best