He did not know, of course, that South had begun with only five hearts and had no way to tell.

He is thinking hard, therefore he began with four hearts.

South was confident that West had begun with six hearts and thus four diamonds.

The Italian auction, shown in the diagram, began with two hearts.

East's discard revealed that West had begun with seven hearts, which was useful information.

On the bidding it was certainly possible that South began with seven hearts.

West was known to have begun with four spades, five hearts and at least two diamonds.

If East began with four hearts, West's play would not matter.

So East must have begun with five hearts or three.

The defense began with two top hearts and a heart ruff.