Pectoralis Major and Minor Stretch.
Pectoralis Major has 3 heads: Upper Fibers in Figure A (can also be done with arms low at sides and lean forward); Middle Fibers in Figure B (elbows must be at 90 degrees); Lower Fibers in Figure C.
Pectoralis Major and Minor are often extremely tight from general activities such as working at a computer, lifting heavy items, doing chest workouts, working on vehicles, driving, etc. When these muscles are overly tight, they will cause pain between the shoulder blades. If you feel pain between the shoulder blades, these stretches will often help.
Stretches must be held until you feel a release, lean further into the stretch until you feel another release. Repeat stretches 2-3 times per day. All muscle heads must be stretched for best results.