Kitten with heart murmur

Hello everyone, I need advice and opinions . I got a VERY playful and active 5-6 months old kitten that I got from the streets when he was barely 2 months old. I took him to the vet yesterday just for a general checkup and the mood was playful until she started listening to her heart. Then she got all serious and worried. She told me he got a quite serious and bad heart murmur to the point where she said she told me to get an appointment with a cardiologist to do an ultrasound to assess the gravity of the problem. She said we need to do extra tests before castrating him because she is not sure he would pull through anesthesia. I'm a very anxious cat mom and I care so deeply about this kitten that I'm worried to death, I've tried to read so many articles online but it's all very confusing and non-conclusive.. my question is, at this age is it possible for the heart murmur to get better with treatment? If not, what is the life expectancy of my kitten? I'm not worried about the price of anything as luckily I live in a country where vet treatments are not extremely expensive so I'm ready and willing to pay for anything I have to do to help him the best I can.

I already got an ultrasound booked for the 8th of February but the anxiety Is eating me alive and I need to know as much as I can on this topic. I will also do any procedures I have to do, no matter the price I have to pay

Thank you to everyone that will help