Hi,
   I can understand your concern.
  * It is not necessary that the next child will have congenital 
heart disease.
So cool down, be positive & try to avoid following things in 
pregnancy,which are said to cause congenital heart problem in babies.
   - Genetic- One of the parents has congenital heart problem makes 50% chances of children getting it. In that case chromosomal analysis cn help to know affection of a child.
  - Viral infections in early 3 months  of pregnancy- Exposure  to infection can be avoided / Flue 
vaccination..    
Rubella vaccination 6 months prior to conception will prevent rubella infection and it's untoward effect on fetal heart.
   - Alcohol & 
smoking in pregnancy - can be stopped.
   - Diagnosis & treatment of 
gestational diabetes will prevent heart problem in new born.
   * apart from this being healthy 3 months before conception(of both partners)
     -healthy lifestyle in pregnancy,
    - regular medical check ups & investigations suggested by doctor ( specially 3D USG of fetus at 5 months)- will help you to give birth to a healthy baby.
   Thanks.