TextBlock Opacity Animation

   
     

<Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
      xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">

    <TextBlock x:Name="txtblk" Text="XAML" 
               FontSize="144pt" FontFamily="Arial Black"
               HorizontalAlignment="Center" VerticalAlignment="Center">

        <TextBlock.Triggers>
            <EventTrigger RoutedEvent="TextBlock.Loaded">
                <BeginStoryboard>
                    <Storyboard TargetName="txtblk" 
                                TargetProperty="Opacity"
                                RepeatBehavior="Forever">
                        <DoubleAnimationUsingPath Duration="0:0:4" 
                                                  Source="Y">
                            <DoubleAnimationUsingPath.PathGeometry>
                                <PathGeometry>
                                    <PathGeometry.Figures>
                                        <PathFigure StartPoint="0 0">
                                            <LineSegment Point="0 1" />
                                            <LineSegment Point="2 1" />
                                            <LineSegment Point="2 0" />
                                        </PathFigure>
                                    </PathGeometry.Figures>
                                </PathGeometry>
                            </DoubleAnimationUsingPath.PathGeometry>
                        </DoubleAnimationUsingPath>
                    </Storyboard>
                </BeginStoryboard>
            </EventTrigger>
        </TextBlock.Triggers>
    </TextBlock>
</Page>