A 3 mm opening in the wall between the upper heart chambers is normal in newborns and can take weeks, months or years to close. A 3 mm opening is called a PATENT FORAMEN OVALE (PFO) and does not qualify to be called a secundum atrial septal defect, It would be highly unusual for a 3 mm PFO to cause any enlargement of the right side of the heart. So either the echocardiogram is being over-interpreted by an adult cardiologist, or there could be something else going on, like some of the pulmonary veins draining abnornally to the right side of the heart instead of the left side of the heart. If your child ONLY has a 3 mm opening and all else with the heart is truly normal, then the need for future surgical intervention would be exceedingly small. So it all depends upon what symptoms your child has. Make sure you are being consulted by a cardiologist who cares for children, not just adults.
Thank you so much for your reply. As you suggested we will consult the cardiologist who cares for the children.
Actually my wife and kid are in India and I came to South Africa for work. She is worrying a lot about my younger son.
Could you please share me your email id so that I can share the copy of the echo report to you. We can get the exact problem of my child and it's severity.