....
<VisualState x:Name="MouseOver">
<Storyboard>
<DoubleAnimation BeginTime="0" Storyboard.TargetName="Element" Storyboard.TargetProperty="(Shape.StrokeThickness)" To="3" Duration="00:00:01" />
</Storyboard>
</VisualState>
...
Yes, but how can I keep the line's original color (defined in the .mxd) and just change the width of the line?