@siddlebittle Hello. I would like to welcome you to Connect. Of course consulting a cardiologist is important when you have chest pain or palpitations. It can be possible to have these symptoms from other issues that are not heart related. Having a tight left side may indicate a problem like thoracic outlet syndrome and that may cause arm pain and shoulder blade pain symptoms and breathing issues. If you also have a cervical spine issues, you may also have neck muscle spasms that can tighten up the area between the neck and shoulder.

I do have TOS and cervical spine issues and had a C5/C6 fusion. TOS may affect breathing and tightness can physically restrict the expansion of the chest. I have done myofascial release to treat this and get my rib cage moving properly or closer to normal again. I have had chest pain caused by muscle spasms and stretching with fascial release has relieved it right away. Patients should not diagnose themselves. If heart issues have been ruled out, a physical therapist who does MFR therapy may be able to ease some of the tightness and pain.

Here is a link to our Myofascial release discussion. There is a provider search at http://mfrtherapists.com/

Neuropathy - Myofascial Release Therapy (MFR) for treating compression and pain
https://connect.mayoclinic.org/discussion/myofascial-release-therapy-mfr-for-treating-compression-and-pain/
Bad posture causes symptoms with TOS by having forward slouching posture that further compresses an area that is already compressed. Compression points are between the scalene muscles on the side of the neck and under the pec minor muscle going into the arm pit. Turning the head can cut off circulation to the arm. My hands used to turn blue and purple and get cold to the touch. Some patients can pass out from turning their heads. Many doctors miss this diagnosis. Typically TOS symptoms are increased at night because of either compressing the shoulder if a side sleeper or neck posture positions or sleeping with an elevated arm raised around should height. A forward head and neck position exacerbates symptoms. Doctor who do diagnose TOS are often thoracic surgeons and Mayo is a good place for this evaluation. When I was evaluated, they had tiny blood pressure cuffs on my fingers and by raising my arm and turning my head they demonstrated a big drop of blood pressure. When they listened to my pulse in my neck, and I turned my head, that pulse stopped. Here are a few links.
https://mskneurology.com/how-truly-treat-thoracic-outlet-syndrome/
https://my.clevelandclinic.org/health/diseases/17553-thoracic-outlet-syndrome-tos
https://www.mayoclinic.org/diseases-conditions/thoracic-outlet-syndrome/symptoms-causes/syc-20353988
Have you heard of thoracic outlet syndrome before?