uses commctrl;
procedure TForm1.Button1Click(Sender: TObject);
var
header: THandle;
begin
header := SendMessage(ListView1.Handle, LVM_GETHEADER, 0, 0);
SetWindowLong(header, GWL_STYLE, GetWindowLong(header, GWL_STYLE)
and not HDS_BUTTONS);
UpdateWindow(header);
end;