Error in gridview chekbox....rectify

I have gridview1 with checkbox column present

checked row in gridview1 should display corresponding details
in gridview2

by using lik this continued...
foreach(GridViewRow g in gv.Rows)
{
CheckBox chkbxx = (CheckBox)g.FindControl("chkSelect");
var value=....
if(chkbxx.checked==true)
{
gv.datasource=value;
gv.databind();
}
}

if i checked 3 rows ,this ll loop inside this foreach and displaying oly the 3rd row details.
Means last records alone displaying.
First two checked detials not showin..why?