What can cause chest pain?

I went to the ER with chest pain and was admitted for two days. The tests all came back normal. The EKG was fine. Cardiac enzymes were fine. X-rays and echo both showed my heart was enlarged. I do have high blood pressure that I treat with medication. They did say I had low potium levels. But should not cause pain in chest. Never found out what the cause of the chest pain was. It wasn't severe. just an achy feeling in my chest that went into my shoulder and left arm. There was no blockage or any sign that I had a heart attack. Does anyone know what could have caused this pain? Anyone experience anything similar?