gridview headers not shown as we scoll down

[kumar p]

hi,
 i have an grid  placed inside an ScrollViewer 

<ScrollViewer Height="300" ScrollViewer.VerticalScrollBarVisibility="Auto" >

<StackPanel>
/here  i have placed an grid
</StackPanel>

</ScrollViewer>

 once i scroll down the grid the headers of the gridview are not shown.is there any way i can fix the gridview headers  so that even i scroll  down the grid the headers are  shown

 the screen shoot will explain better image.

any help would be greatly appreciated.
 thanks