C#

<Path.Style>
    <Style TargetType="Path">
        <Style.Triggers>
            <DataTrigger Binding="{Binding InProgress}" Value="True"  >
                <DataTrigger.EnterActions>
                    <BeginStoryboard>
                        <Storyboard AutoReverse="True"
 RepeatBehavior="{Binding Path=InProgress, Converter={x:Static Converters:BooleanToRepeatBehaviourConverter.Instance}}" >                                                
                            <DoubleAnimation To="0.125" Duration="0:0:0.12"
 Storyboard.TargetProperty="(LayoutTransform).(ScaleTransform.ScaleX)" />
                            <DoubleAnimation To="0.125" Duration="0:0:0.12" 
Storyboard.TargetProperty="(LayoutTransform).(ScaleTransform.ScaleY)" />
                        </Storyboard>
                    </BeginStoryboard>
                </DataTrigger.EnterActions>
            </DataTrigger>
        </Style.Triggers>
    </Style>
</Path.Style>

public class BooleanToRepeatBehaviourConverter : IValueConverter
{
    private static readonly IValueConverter instance = new BooleanToRepeatBehaviourConverter();

    public static IValueConverter Instance
    {
        get { return instance; }
    }

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return (bool) value
                    ? RepeatBehavior.Forever
                    : new RepeatBehavior(0);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}