I Was In The Hospital For Treatment For Chest Pressure

I was in the hospital for treatment for chest pressure and pain which lasted 20 minutes at a time. Many tests run and ruled out heart problem and had an angioplasty done. Sent home on blood thinners, and heart relaxer, Imdur. Plus nitroglycerin. EKG also normal. I am wondering what else could be causing left chest pain under my left arm mostly?