Thanks for your question on Health Care Magic. I can understand your concern. Since he had five bypass operations, his heart functions must have low. So possibility of fluid retention in the body is more. This causes Pulmonary edema (fluid congestion in lungs). This causes breathlessness on exertion. So he is mostly having Pulmonary edema. He need diuretic drugs to prevent fluid retention. Other cardiac supportive drugs like beta blocker, ACE (angiotensin converting enzyme) inhibitors and digoxin are useful in his case. So rays or glycerine nitrate will not help much during breathlessness. Above mentioned drugs will help in preventing breathlessness. So consult cardiologist and discuss about starting these drugs. Hope I have solved your query. I will be happy to help you further. Wishing good health to your husband. Thanks.