Giving him one more trick, and beating the contract by three instead of four, was unlikely to be significant.
In that case we can beat the contract if he takes the heart ace now and plays another diamond.
West would have beaten the contract if he had returned a heart at the fifth trick.
Further analysis shows that West could have beaten the contract with a different lead.
This proved to be the only way to beat the contract.
A diamond lead was the only one to beat the contract.
Beating the contract won the board for the Shugart team.
West could now have put up the heart king and beaten the contract in various ways.
Almost any lead would have beaten the contract, including the heart king.
This established two winners in the West hand and was apparently good enough to beat the contract.