If this were a heart issue, you would be having much more serious symptoms and it would be on the left side.

What you’re describing sounds like a muscle strain or a pinched nerve.

I think you need to talk to your doctor or someone that works with your doctor. There are a number of things I could think of that might be causing the problem and you need someone who knows what they’re doing.
I had never heard of pain going down the left arm only it could be either arm as far as I am aware of.
You need to do some homework to figure this out and I wish you the very best

Years ago, I experienced severe pain in my left arm. As it turns out, I had ruptured a cervical disc in my neck and ended up having to have surgery to replace it. The pain from a ruptured disk is unbearable, so unless you are in extreme pain, it's unlikely to be caused by a ruptured disk, but you may well have HERNIATED one of the cervical disks and it is pressing (pinching) the nerve going to your right arm. A doctor should be able to run a few tests (xray, mri, etc.) to determine if that is what is causing your pain. I hope this helps. Hope you get some answers soon.