Severe pain in left shoulder/arm and down left side?

Varable: Does it hurt with shoulder movement? It may be joint, shoulder , muscle in cause. If not, concerns are heart, lung and either way you need a full history and appropriate exams.

See doctor: Its important to establish a diagnosis. Shoulder/arm/radiating pain could be from 1) referred sources including: neck, abdomen, and heart. 2) shoulder sources include: arthritis, labral tears, instability, tendinitis, rotator cuff tears, bursitis, painful bony spurs etc. Therefore proper diagnosis is essential to stopping the pain. See an orthopedic surgeon.