Holland international Heitinga has impressed in both defence and midfield for the Toffees during the second half of the campaign.
Moyes admits it took the 26-year-old time to settle after his £6million move from Atletico Madrid last September but now feels he is showing his true value.
Moyes said: "I think Johnny Heitinga had a difficult time when he first came because the team wasn't playing very well. I also think he was completely shocked by the speed of the Premier League. I think he had cramp in the first two games.
"He was taken aback by it but I think he has settled into it now. He is a really good professional, a very serious man about his football.
"He has done a couple of good jobs for us at the back and in midfield."