Petit Verdot is, as far as we can ascertain, a Bordeaux grape long before Cabernet Sauvignon.
It provides backbone and structure to Bordeaux blends but is not widely used anymore as it ripens most later than the other grape varieties (in some years it just doesn't ripen in time so is omitted from the classic blend). However, in good years, you will see up to 6 or 7% of Petit Verdot in the blend of some classed Growths (Cantemerle has normally between 4 and 6% in it';s blend.
Try our Petit Verdot by Belle-Vue (if still available) - 100% Petit Verdot and scoring 91+ on Robert Parker's Wine Advocate.
and only €35 per btl (don't tell my Scots Granny!)