What can cause pain in the upper left part of my back?

Many things: Although by far the most common cause is muscular in nature, other causes include heart disease (coronary artery disease), lung disease and spinal disorders, to name just a few. If the pain has been persistent, it is best to be evaluated by your personal family physician. Another option is to see a physical therapist who should be able to tell you if it is simply musculoskeletal in nature.

Muscle: Muscle strain or injury.