Heitinga, who played alongside Everton's Steven Pienaar at Ajax for five years, is excited about the challenge.
"It's a nice club and a club with a big history. I saw a lot of Everton games last season and they have a strong team," he said.
"I spoke with the manager earlier and the feelings were good."
Heitinga helped the Amsterdam club win the Eredivisie title twice and the KNVB Cup three times, and was voted the Netherlands' player of the year in 2008 before joining Atletico that summer on a five-year contract.
Everton were keen to reinforce their defence having sold central defender Joleon Lescott to Manchester City for about £22m and given that Phil Jagielka is still sidelined with a knee injury.
They also signed defender Sylvain Distin, 31, from Portsmouth on a three-year deal for an undisclosed fee on Friday, plus Russia midfielder Diniyar Bilyaletdinov, 24, from Lokomotiv Moscow for an again undisclosed fee three days earlier.
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