@Natsubi - welcome to the blog - I hope we will be able to help you thru any problems you may have.
There is actually a long history of heart problems and other major side effects (specially with some chemo treatments) and I've experienced 'lesser' heart issues myself & am now on a 1/2 beta blocker to control palpitations/KERTHUNK! I seriously thought I was having a heart attack & called the ambos!
If you are not happy with your Onc believing your side effect issues - you are allowed to change Oncs. I did as my first male Onc was most dismissive of my side effects with Letrozole.
You need to be able to discuss issues with your Onc without feeling fobbed off. I am also in the public system in regional NSW and had no problems in swapping Oncs -and also see the same one all the time, unless she is ill or away.
Have you seen a heart specialist & had all the tests & got it documented? Did you have chemo? Some chemos are proven to cause major heart problems .....
take care, get checked out, & consider changing your Onc, I reckon! xx