Like XAMLeLi already mentioned
you should use ControlTemplate
for the TabControl
here is the working example (here is the Original)
<TabControl TabStripPlacement="Left" Height="60">
<TabControl.Template>
<ControlTemplate TargetType="TabControl">
<StackPanel Orientation="Horizontal">
<ScrollViewer VerticalScrollBarVisibility="Visible" HorizontalScrollBarVisibility="Disabled" >
<TabPanel x:Name="HeaderPanel" Margin="2,2,2,0" IsItemsHost="true" />
</ScrollViewer>
<ContentPresenter x:Name="PART_SelectedContentHost"
SnapsToDevicePixels="{TemplateBinding SnapsToDevicePixels}"
Margin="{TemplateBinding Padding}"
ContentSource="SelectedContent"/>
</StackPanel>
</ControlTemplate>
</TabControl.Template>
<TabItem Header="Visible" >
<Grid Width="100" Height="100" Background="Blue"/>
</TabItem>
<TabItem Header="Visible"/>
<TabItem Header="Visible"/>
<TabItem Header="inv" Background="Red">
<Button Content="blubb"></Button>
</TabItem>
<TabItem Header="inv"/>
<TabItem Header="inv"/>
<TabItem Header="inv"/>
</TabControl>