What Causes Sharp Pains In The Arms And Under The Breast?

Hi I am 23 and my heart has been racing for awhile now. One night my heart went crazy,I felt dizzy,my hands got sweaty and so I went to the hospital theydid all the test and found nothing wrong and said I might be having panic attacks but after awhile I have had similar episodes but now I have sharp pulsing pains in both arms and under the breast