How to Cope with Fear of Heart Defects in Children?

I'm feeling so nervous and scared. My friend on fb had his daughter early cause of a hole in her heart and other heart problems. well she passed away yesterday at 6 days old. I couldn't help but cry for him and his gf. My 2nd daughter was born with a hole in her heart and still has it. Now I'm scared and worried my son will also have one and maybe won't be as lucky as his big sister...