Hello @alina96, and welcome to Mayo Clinic Connect!
First let me say how sorry I am that your little baby is going through this. And you are too! It has to be so stressful living with this disorder and knowing he will need open heart surgery in a short time. I suppose the blessing is he will not remember having the open heart surgery, and that's a good thing! I had open heart surgery and remember almost everything!
A mother's instinct to protect her baby is so strong, and you have a lot of real issues to cause you fear.
Fear would be natural, so there is no shame in having fear. Try to learn as much as you can to know what your little one is facing. Being his best advocate is the greatest thing you can do for him and you!
Have you read this from the Mayo Clinic?:
https://www.mayoclinic.org/diseases-conditions/tetralogy-of-fallot/symptoms-causes/syc-20353477
While we wait for others who may have real experience with this to respond to your question, how is your little one doing now? How often do you see his pediatric cardiologist?