[jQuery] Var in the Succes: part of Ajax

Hi everyone !
My problem is simple.
Here is my code :
function ajax_test(){
    anc_pv = $('.pv_act').attr("pv");
    $.ajax({
     type: "GET",
     url: "ajax_test.php",
     data: "",
     dataType: "html",
     success: function(data){
        alert(anc_pv); // But it show "undefinided"
     }
    });
};
Any idea, someone ?
Thanks in advance ! Bye !