[jQuery] jqModal clear fields

Hi all
I use the jqModal, and I want to clear some fields in the modal window
after opening. Cant get it to work so some advise would be perfect.
Like this
    var open = function(hash){
        $("#myFiled").val('').show();
    };
    $('#dialog').jqm({
        overlay: 8,
        onShow: open
    });
/ johannes