hi after open heart surgery patient remain confined to bed for 2,3 days and after that he starts to ambulate slowly over weeks, There are a number of things that can cause stomach bloating following heart surgery. They include fluid build-up , constipation ,limited moments,as he will start to ambulate bloating and fullness will go away drug like pantoprazole and rabeprazole an be given if he is feeling more problem. constipation can be treated with laxatives like lactulose for the time being. add fibres to his diet avoid oily and fatty food give him light food till he returns back to normal activities thank you