Private Declare Function SendMessage Lib "User32" Alias "SendMessageA" _
    (ByVal hWnd As Long, ByVal wMsg As Long, _
     ByVal wParam As Long, ByVal lParam As Long) As Long
 
Private Sub deshacerCmd_Click()
    Const EM_CANUNDO As Long = &HC6
    Const EM_UNDO As Long = &HC7
    '
    ' se comprueba si se puede deshacer
    If SendMessage(Text1.hWnd, EM_CANUNDO, 0&, 0&) Then
        ' si es así, se deshace
        SendMessage Text1.hWnd, EM_UNDO, 0&, 0&
    End If
End Sub