7S can be forcibly won with five HCP:
If West leads a spade, South takes the ace. If West leads a heart, North ruffs and leads a spade to the ace. Otherwise South ruffs low and leads the ace of spades.
South can then ruff two hearts (or three, if desired), using spades or diamond ruffs to return to hand, and run the hearts until North has nothing but spades.
A slightly more detailed explanation, for those not familiar with bridge:
On the first trick, if West leads a spade (the king), North will have to play a spade 2-8 (all equivalent), East will be required to play the queen, and South can play the ace and take the trick. Neither East nor West will have any spades left.
If West leads anything else, it will be in a suit that either North or South doesn't have. A player without any card in a suit that's led may then play any card that is in their hand, including a spade (if one is possessed). The highest spade played on a trick, if any, will take the trick. Thus, either North or South will be able to play a spade on the first trick and then lead a spade, forcing East and West to play the king and queen while South takes the ace, again leaving East and West without any spades.
If South plays a suit that North doesn't have but the opponents do (hearts), North will be able to play a spade which will prevail over any heart that East or West plays. The first time South takes control, it will be after spades have been led once, and South will have played at most of his spades prior to that, so South will have at least two high spades left. Thus, the first two times North trumps a heart, North will be able to lead a spade that South can capture to regain the lead.
The first two times hearts are led, the opponents will each have to play one. After that, nobody except South will have any hearts; if South leads hearts and North discards diamonds until there are none left, the hearts will take tricks. At that point, North will have nothing but trump cards, so on every remaining trick, no matter what North and South do, either North will lead a trump which is captured by a higher trump in South's hand, South will lead a heart which gets captured by a trump in North's hand, or North will lead a spade upon which South discards a heart.