Page "Yu-Gi-Oh! Trading Card Game" Paragraph 39

When a monster card " declares an attack ", one of the opponent's monsters is selected as the target.

At this time, the ATK points of the attacking monster are compared with the relevant ATK or DEF points of the opponent's targeted monster ( depending on whether it is in Attack Position or Defense Position ).

The monster card with the lower points is destroyed and sent to the Graveyard.

Subsequently, the victorious monster may have the attack points of the defeated monster subtracted from the pool of that monster's attack points.

If the destroyed monster card was in Attack Position, then its owner will lose Life Points equal to the difference between the two monsters ' points.

For example, if Mystic Tomato ( which has 1400 ATK and 1100 DEF ) attacks an opponent's Sangan ( 1000 ATK and 600 DEF ) in Attack Position, then the opponent's Sangan is destroyed and he or she loses 400 Life Points.

However, the owner will not lose Life Points if his or her monster card was in Defense Position.

In the previous example, if Sangan had been in Defense Position ( placed in a horizontal orientation ), then it would still be destroyed by an attacking Mystic Tomato but its owner would not lose Life Points. However, If the Defensive Points of a Card ( for this example the card Mystic Elf, which has 800 ATK and 2000 DEF ) is higher than the ATK points of the attacking Card, the owner of the attacking card will lose life point to the difference of each number ( If Mystic Tomato attacked the Mystic Elf in Defense mode, the owner of Mystic Tomato would lose 600 life points ), but the attacking monster is not destroyed.

No Cards are destroyed after the end of an attack subject to a card effect ( like D. D Warriors effect which removes both this card and the attacking card from play )