Animating window loading in xaml

I have this xaml:

    <Window.Triggers>
        <EventTrigger RoutedEvent="Window.Loaded">
            <EventTrigger.Actions>
                <BeginStoryboard>                    
                    <Storyboard BeginTime="0">
                        <DoubleAnimation Storyboard.TargetName="me"  Storyboard.TargetProperty="Top" From="0" To="275" AutoReverse="true" BeginTime="0:0:0" Duration="0:0:2" RepeatBehavior="0:0:4" />
                        <DoubleAnimation Storyboard.TargetName="me" Storyboard.TargetProperty="Left" From="0" To="350" AutoReverse="true" BeginTime="0:0:0" Duration="0:0:2" RepeatBehavior="0:0:4" />
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger.Actions>
        </EventTrigger>
    </Window.Triggers>

which works fine - when the window is loaded it moves down and across the screen and then back. But if I change the TargetProperty values from "Top" to "Height" and "Left" to "Width", absolutely nothing happens. I was hoping that the window would expand and then contract.

Can someone explain what it is I'm not understanding??

Thanks for any suggestions!

Ade