Dim MouseIsDown As Boolean = False
'(...)
Private Sub do_mouseDown(ByVal sender As RectangleShape, ByVal e As _
  MouseEventArgs) Handles Rectangleshape.MouseDown
  MouseIsDown = True
  RunLoop()
End Sub
 
Private Sub do_mouseUp(ByVal sender As RectangleShape, ByVal e As _
  MouseEventArgs) Handles Rectangleshape.MouseUp
  MouseIsDown = False
End Sub
 
Private Sub RunLoop()
  While MouseIsDown
    'Schleife
  End While
End Sub