XAML:

    xmlns:tk="clr-namespace:System.Windows.Controls.DataVisualization.Charting;assembly=System.Windows.Controls.DataVisualization.Toolkit" 
    Title="One Pie" Height="350" Width="525" Loaded="Window_Loaded">
    <DockPanel LastChildFill="True">
        <tk:Chart x:Name="chart" >
            <tk:Chart.Series>
                <tk:PieSeries ItemsSource="{Binding}"
                    DependentValuePath="Value"
                    IndependentValuePath="Key"
                    Title="Pet Preference" IsSelectionEnabled="True" />
            </tk:Chart.Series>
        </tk:Chart>
    </DockPanel>


CS:
using System.Windows.Controls.DataVisualization.Charting;

private void Window_Loaded(object sender, RoutedEventArgs e) {
   chart.DataContext = new KeyValuePair<string, int>[] {
         new KeyValuePair<string, int>("Dog", 30),
         new KeyValuePair<string, int>("Cat", 25),
         new KeyValuePair<string, int>("Rat", 5),
         new KeyValuePair<string, int>("Hampster", 8),
         new KeyValuePair<string, int>("Rabbit", 12) };
}