In your style:
<YourControl.Triggers> <EventTrigger RoutedEvent="YourControl.Loaded"> <BeginStoryboard> <Storyboard> <DoubleAnimation Storyboard.TargetProperty="Width" From="0" To="150" Duration="0:0:5" /> <DoubleAnimation Storyboard.TargetProperty="Height" From="0" To="100" Duration="0:0:5" /> </Storyboard> </BeginStoryboard> </EventTrigger> </YourControl.Triggers>
source share