West led the heart ace, and for want of anything better continued with the king.

But after winning with the heart ace, South did not give up.

South held up the heart ace, and West could well have continued.

He does so, which is right when East has the heart ace.

It would have been wrong if West had held the heart ace, but that was less likely.

He led to the heart ace and played the ten.

Looking at the four hands it is easy to see that West should lead the heart ace.

But what would have happened after a normal lead of the heart ace?

South led to the heart ace and continued the suit.

Instead he led to the heart ace and was on the road to success.