Вариант раз

Canvas x:Name="Canvas" Background="Transparent" Height="25"
                VerticalAlignment="Top">
            
                
                    
                        
                            
                                
                                    
                                
                            
                        
                    
                
            
        

http://axedeos.blogspot.ru/2012/11/wpf.html

Вариант два, с заданием в коде и с паузой

  
    
    
      
      
      
      
    
    


public partial class StopAnimationWindow : System.Windows.Window
{
    AnimationClock clock;
    public StopAnimationWindow()
    {
        InitializeComponent();
    }
 
    private void StartAnimation(Object sender, RoutedEventArgs e)
    {
        DoubleAnimation animation = new DoubleAnimation();
        animation.Duration = new Duration(TimeSpan.FromSeconds(5));
        animation.To = 500d;
        animation.From = 0d;
        clock = animation.CreateClock();
        rect.ApplyAnimationClock(Rectangle.WidthProperty, clock);
    }
 
    private void PauseAnimation(Object sender, RoutedEventArgs e)
    {
        clock.Controller.Pause();
    }
 
    private void ResumeAnimation(Object sender, RoutedEventArgs e)
    {
        clock.Controller.Resume();
    }
 
    private void StopAnimation(Object sender, RoutedEventArgs e)
    {
        clock.Controller.Stop();
    }
}

http://social.msdn.microsoft.com/Forums/vstudio/en-US/5eb35986-4666-43f4-9e88-e940bf464ff5/how-to-pause-animation