Okay here's the deal I have had this dull aching pain in my left pectoral muscle on and off for the last few years. I'm male, 22, 5'9, 180, smoked casually for 6 years and now no longer smoke, weekend drinker. I am in excellent shape and ride bike about 10 miles a few times a week and also go to the gym and lift weights twice a week. The pain also happened more frequently while I was stressed during last semester of school. I never get any chest pain while exercising. I don't think it has anything to do with my heart but was am not 100 percent. Also my left pectoral muscle is for some reason larger than my right and was thinking this may have something to do with it. I have not seen a doctor about it. I also still have a grade 2 heart mummur from when I was young, but have been told it's innocent and never get fatigued while intensly exercising so I don't think this has anything to do with it. Any good advise.