What does the surgeon say about it, or the cardiologist? If need be, they can do several diagnostic tests to determine that all is well, or if there is a problem. It is also possible to measure the oxygen saturation volume and that's as easy as pie to do.
A certain amount normal and is to be expected and will gradually go away with the use of the spirometer and walking to get some aerobic benefit and you really have to force yourself to do that because the natural instinct is not to. The heart and lungs have to shape up.
But if the breathlessness is significant, better hit the phone to the doctor's office. They're the only ones who can figure it out.
Good luck and let us know how things go.