I have this pain under my left breast ?

If a lump or mass: is present, you should see your doctor. If it is below the breast in the chest wall it could be a muscle or rib pain. If worse with activity, could be your heart. If persistent or worse, see your doctor.

Can be : concerning, if mass in breast, or could be rib or muscle pain, or if deeper could be heart related, you really need to see your doctor.

Just 4 words?...: "Pain above left breast" means different things to different people. One's primary care can examine to see what a particular person means by "above" a breast. Usually, that would be the area between the collar bone and the breast. In that area, in a man in his 30's, are his pectoral muscles, ribs, linings of the ribs, lung and its lining, skin, nerves, blood vessels, etc... Details are important!