welcome to HealthcareMagic
You should be happy to have one girl and a boy inspite of having mitral valve prolapse
.If the doctors as well as your family members are saying not to take risk of another pregnancy
then i guess it is enough reason not to go for it.Still if you think logically it is like you are risking life of mother of two kids just because you want to have another.Heart disease
is risky and you have taken your chances so better to avoid pregnancy.