I Am Periodically (maybe Once A Month) Having A Sensation

I am periodically (maybe once a month) having a sensation that feels like a worm wiggling in my heart. I am a stage 3 breast cancer survivor (5 years cancer free). The cancer was in my left breast. I had 6 rounds of chemo, Double mastectomy, radiation and 12 months of Herceptin. Any idea what the "worm sensation" could possibly be?