An Ace of any suit causes the player to play again. One of the best ways to lose your cards faster.
The downside of the Ace is that the game cannot be won with an Ace as the last card. This is because you MUST play again after playing an Ace. If you come to this weird situation, you will have an empty hand (no cards) and still be expected to play. But since you have no cards to play, you will have to draw from the Croupier.
Be warned, at this point you will not be able to announce last card before saying "Pass", because raising the flag only works if you play a card after it. So think about your Ace beforehand and do not leave it as your very last card.