Top left side of chest is randomly hurting. when taking deep breaths, top left side hurts. when extending my arm, my heart area/or muscles tighten.

Chest Pain Causes: The first thing you may think of is heart attack. Certainly chest pain is not something to ignore. But you should know that it has many possible causes. http://www.webmd.com/pain-management/guide/whats-causing-my-chest-pain

L chest pain: May be tendonitis ( pectoralis/biceps ) or costochondritis( inflammation of joint of ribs to sternum ) or AC joint. Could try Motrin if not allergic to ease the discomfort, rarely autoimmune process, breast lesion( rather young ) or pericarditis or clot f/u w/ doc , ESR ,EKG, d-dimer, sono, echo. http://www.mayoclinic.org/diseases-conditions/costochondritis/basics/definition/con-2002445