Hello and welcome to the forum. Thanks for your question and we are glad you had a successful outcome to your surgery 27 years ago! Here is information on VSD or Ventricular Septal-defect. https://www.mayoclinic.org/diseases-conditions/ventricular-septal-defect/symptoms-causes/syc-20353495 Basically this is a hole in the heart and it most often forms during fetal development of the organ. The exact cause is really unknown although genetics and environmental causes could play a role and does often run in families. So, when your partner is pregnant, talk to their obstetrician so that they are aware. Prenatal care will be important as it always is but especially in this circumstance.
Best of luck to you.
Best thing is to see a geneticist.