Subitmes are Items of an Item. ListView1 in your case does not contain subitems. ListView1.Items(0) however would contain SubItems.

I like to add items by using a listview item. This to me makes the code much more readable.

Code:
        Dim LSingleItem As ListViewItem
        LV.Clear()
        LV.View = View.Details
        LV.GridLines = True
        LSingleItem = LV.Items.Add("Text")
        LSingleItem.SubItems.Add("SubItem Text")

or.....

        LSingleItem = LV.Items(1)
        LSingleItem.SubItems.Add("SubItem Text")
Where LV is my listview.