I would recommend you ask his Doctor to have his heart Doctor do a echocardiagram. Sometimes people develope pleural or pericardial effusions. (fluid around the lungs or heart). After my surgery to remove my left lung, I had pain and breathing problems that took almost 8 months for the Drs. to determine it's cause. It often takes just the right test to see what's going on. Just a thought and good luck to you!