How safe is it for patients who have undergone angeoplasty to go on international flights exceeding 20 hrs?

My mother aged 58 had an Angioplasty done in Apr-2006. She has been having high blood pressure since 1993. Yesterday she was admitted in a hospital in India coz she was complaining of severe cold and experienced chest pain and fainted. In Nov'07, she is planning to visit me in the US. The travel time and duration of flight will be over 20 hrs. I am worried about this travel coz my uncle got a heart attack and expired while landing from a flight on his way from Kuwait to India. Is it safe for my mother to travel?