Code

                    <Button Margin="1" Padding="2" HorizontalContentAlignment="Left"
                            Style="{StaticResource ToolBarButtonBaseStyle}"
                            Command="{x:Static ApplicationCommands.Print}"
                            CommandTarget="{Binding ElementName=MyDesigner}">
                        <Button.Content>
                            <Grid>
                                <Grid.ColumnDefinitions>
                                    <ColumnDefinition/>
                                    <ColumnDefinition />
                                </Grid.ColumnDefinitions>
                                <Image Source="/Layout/Images/Print.png" Width="16"/>
                                <TextBlock Margin="3,0,3,0" Text="Print" VerticalAlignment="Center" Grid.Column="1"/>
                            </Grid>
                        </Button.Content>
                    </Button> 

Code

public MainWindow()
{
   InitializeComponent();

   CommandBindings.Add(new CommandBinding(ApplicationCommands.Print, Print_Executed));
}

        private void Print_Executed(object sender, EventArgs e)
        {
            flowchart.PrintOptions.DocumentName = "Flowchart";
            flowchart.PrintOptions.EnableImages = false;
            flowchart.PrintOptions.EnableInterior = true;
            flowchart.PrintOptions.EnableShadows = true;
            flowchart.PrintOptions.Scale = 100;
            flowchart.Print();
        }