Rapid Growth

My husband was born with a hole in his heart along with an innocent murmur.  He is very athletic, plays basketball. About three years ago, he went to the doctor because he was having severe chest pains. They did all the necessary work and found that one of his valves was not working properly, and sent him on his way. And now he's having chest pain and finds out today that his heart is 14.5 cm thick.  And they mentioned how the thicker it gets the less it can pass through electrical charges to pump blood.  My question is... how long does it take for the heart to continue to thicken?  The last thing that I want is for us to be out at the park with my daughter and not realize that over the next few years, his heart continued to grow and  he falls over!   I guess I don't understand, why didnt the doctors notice this 3 years ago, or within the last 3 years has his heart thickened enough to cause concern.... and if thats the case... how much longer could I have with him?