Hmm, I agree with atonicat. ECG and heart test are great, but this sounds like it's more related to the cervical spine area, particularly C5/6. Did you injure your head or neck before these symptoms started? It could also be just a past of degenerative disk disease.
My cervical neck problems began to show up in just a xray, I still am wanting/waiting to get other apporpriate tests done. If you have good insurance/good doctors I would ask/suggest a neck/spine xray and/or mri. A chiropractor might be able to shed some light.
Have you had an MRI of your C and T spine? Radiating pain is usually caused by nerve impingement.