<s>[INST] My friend has a been experiencing pains in his chest... he says that his heart hurts when hes running or excersising...It just started and im worried. He is 15 years old at 6 foot even, and he has been a very active person all his life. He plays basketball football and baseball. Any suggestions on what might be going on with him? [/INST] Thanks for your question on Chat Doctor. I can understand your friends situation and problem. Possibility of musculoskeletal pain is more but better to rule out heart related diseases because he is having left sided chest pain. So first get done ECG and 2d echo to rule out cardiac diseases. If both these are normal then no need to worry about heart diseases. Musculoskeletal pain is more likely in his case. So ask him to follow these steps for better symptomatic relief. 1. Avoid heavyweight lifting and strenuous exercise. 2. Avoid bad postures in sleep. 3. Avoid movements causing pain. 4. Apply warm water pad on affected areas. 5. Start painkiller and muscle relaxant Chat Doctor.  He will mostly improve in 1-2 weeks. Hope I have solved your query. Wishing good health to your friend. Thanks. </s>