I also had A/C - T, plus Herceptin. I had an echocardiogram before starting chemo, developed an arrythmia after nearly five months of chemo and have had echocardiograms annually since. Herceptin can possibly cause damage to the heart wall (none in my case) and the arrythmia is stable and manageable. It was initially blamed on chemo, particularly after surgery, but may be a combination of factors. My gym wanted a certificate from my cardiologist, which was no problem (it's not specialist). My general heart health, apart from the irregular heartbeat, is fine. Best wishes