Oh, I am so sorry to hear about your kitty Noah.
My kitty (Kedi, 8 years old) was diagnosed with a enlarged heart and rapid heart rate back in March. His lungs were aslo filled with fluid, so he was also having a hard time breathing.
Long story short, he is on 2 types of meds now and feels great! When I started giving him meds, he was back to his old self within a week!
There are alot of things they can do now for animals with heart problems, so I am sure your kitty will be fine with treatment.
Let us know how things go at the vet.