we Select multiple indices from list boxes . the listbox have propery of GetSelectedIndicdces . Which return all selected indexes .
so code is like
int[] _SelectedIndexes = lstBlog.GetSelectedIndices();
foreach (int Y in _SelectedIndexes)
{ Response.Write(this.lstBlog.Items[Y].Text + ” “ + this.lstBlog.Items[Y].Value );
} where lstBlog is name of listbox