checked and unchecked always false

Hi, I have checkbox and want to do something in my code depend on is isChecked true or false. So, here is the code:  

Private Sub My_Check(sender As Object, e As RoutedEventArgs) Handles My_Check.Checked, My_Check .Unchecked

MsgBox(My_Check.IsChecked.ToString)

End Sub

I can check and uncheck it million times, but IsChecked property is always False. Why?..

Aleksey