My bestfriend's one year old daughter was also born with a congenital heart disease. The baby has a hole in her heart and one of her major arteries is too narrow, putting lots of pressure on her heart (I don't know the name of this condition). She has gone thru 2 ops in the last 1 year and yes, she is developing very slowly. She is barely sitting up now and has only just started moving a little with her buttocks but it takes so much of her energy. She gets very exhausted very fast. I think she will probably be delayed in development like your son too. Didn't your doctors advice you abt your son's development? I'm not sure, but I think babies wt congenital heart problems do develop slower than normal kids as I've heard from other ppl too. The doctors attending to my friend's kid told her this is normal and to anticipate it. Hope this helps but do definitely talk to your son's doctors if it is normal and on what you can do to help him. Lots of prayers and luck with his development...