Dear Durwank,
Typically, a 3 mm ventricular septal defect is usually so small that it does not cause a problem and does not need surgical repair. It also is not involved as the cause of his colds, if it is that small. If he does not get out of breath or sweaty easily with activity, he should be well. I cannot say for sure without seeing your child exactly what his story is, and why his growth is delayed. Your cardiologist should be able to tell you whether the defect is causing him to be symptomatic from this. There are many patients who have small VSDs remain open into adulthood; it does not shorten their lifespan. It is important to maintain good dental hygiene to prevent an infection of the heart, though.
Hi, I would like to know the age of your child. It is not always required to get an open heart surgery. As it is u mentioned the size to 3mm I think it may close on its own but you will be required for taking your child for regular follow up with your pediatric cardiologist. Secondly I also would like to know the location of VSD like it is muscular, membranous or apical in ventricle. So trust god and please follow as you are advised by your cardiologist. Take care.