Already taking Amiodarone for heart.

My mother (78) was admitted with infections 5 out of the six FEC chemo cycles. (Even with two white cell boosting jabs). One episode resulted in her heart beating dangerously fast and was prescribed Amiodarone that she continues to take. Her Herceptin treatment is due to start on Friday, (she has had the required heart scan)but I am worried that there is obviously a heart problem before she even starts. The oncologist wasn’t aware that she had asthma until it was pointed out and now I wonder if she has picked up about the Amiodarone. Whilst Mum was in hospital it was obvious that the Cardiologist thought the problem was due to the chemo, whilst the oncologist felt that chemo gets the blame for everything. The follow up Cardio appointment isn’t until August (arranged before Herceptin was ever mentioned), so we can’t get advice there. Has anyone heard of a similar ‘combination’?