Hello, There are several causes for this kind of shortness of breath (called dyspnea with exertion). The main causes are congestive heart failure (CHF) and something wrong with your lungs, such as chronic obstructive lung disease (COPD), asthma, or other lung diseases. Things that might make me think of CHF would be if you had swelling in your lungs or if you got short of breath when laying down. Things that would make me think of a lung problem like COPD would be if you had a history of smoking or had a persistent cough. Often it is not clear what the cause is until further testing is done. For patients with your symptoms, I would initially test your blood to check for anaemia, kidney, heart, or thyroid problems, check your oxygen when walking, get a chest x-ray to look for anything abnormal, and a breathing test to check your lung capacity. Further testing would be based on those results. Hope I have answered your query. Let me know if I can assist you further. Take care Regards, Dr Aaron Branch, General & Family Physician