Good morning, Amy, While our cancer treatments are life saving they can come with some pretty serious side effects of their own. Chemo and radiation treatments can both have an impact on our hearts. So it’s a bit of a surprise that your cardiologist is flippant about your concerns.
It’s important to listen to your gut instincts and at least get a second opinion. Do you have the ability to switch doctors? Is there a larger teaching hospital you could try?

I realize you’ve already seen this discussion by another members regarding radiation induced heart disease and hopefully read the entire thread. As you can see, you’re not alone.
I’ve also found some other sites discussing your concerns and posted those below.

You said medication is helping. What tests have you had run to rule out heart related issues?

@amymichc Welcome to Mayo Clinic Connect.
Living in the Pacific Northwest, I am not sure how far you may be from Oregon Health and Science University [OHSU] in Portland area, a great teaching hospital. It is ranked Number 1, and I know several people who have gone there. My husband travels the 4 hours to go there annually for his kidney transplant checkup; we live in southern Oregon.

In the Seattle area is Harborview Medical Center, part of the University of Washington system [but being in mid-Seattle, it is a real pain to access] My sister worked there as an RN for 35+ years, and her commute was always a nightmare!

If you feel you need to get a second opinion, then follow your gut! Cardiac issues know no age range, is my thought. I recall a specialist telling me the same thing a couple decades ago about a condition I have, and my response was to cock my head over to one side and tell him. "Well, I just proved you wrong!"

I hope you will return if you have nay more questions, and let me know what you decide.
Ginger