I know herceptin can enlarge the heart. I have had this problem, but not so bad that I had to stop. I get a echo every few weeks so this can be watched. I just finish my last Taxol treatment with the herceptin. I will continue for a total of 52 weeks having herceptin every 3 weeks.That last treatment with taxol & herceptin my heart started to race. I could not feel this, but the monitor was reading a high heart rate like 156. They did an ekg to play it safe and all was well with that. They kept me for 2 hours until the rate went down to 124 which is still high. Doctor did not know why this was going on. Yesterday, I was at first Rads appointment and heart rate not so bad 102 but it should be below 100. Has any one had this and what was the cause.