<s>[INST] Hi. i am a healthy 18 year old girl and i have been exercising for basically my entire life. I havent had many problems other than a small heart valve leak but i had an ekg done and was cleared to exercise. Yesterday while running pretty vigorously on the treadmill i began to have a sharp pain in my right lung every time i tried to breathe. I immediately stopped running and the pain subsided within a couple of minutes. Any idea what may have caused this? I am not sick and feeling totally fine today. [/INST] Thanks for your question on Chat Doctor. Since you have done ECG recently, and it is normal, no need to worry much for cardiac cause. Your age is also very young for cardiac diseases, so cardiac cause is less likely for your acute sharp chest pain. In my opinion it is muscular pain only, because of sudden muscle pull. And sudden relief from pain is also favouring muscular cause more. So try to follow these steps for better symptomatic relief.1. Avoid strenuous exercise.2. Avoid heavyweight lifting.3. Avoid movements causing pain.4. Take good painkiller and muscle relaxant.5. Apply warm water pad on affected site if appears again. </s>