Hello,
last night I/we played Cash-game NL/Hold'em,1/2,
pre-flop player1raise 12, player 2 raise 25,player 1 call, two player, flop came, player1 bet 20/ player2 raise 48, player 2 show an ace!On purpose!
My question:May you do this or is it always different? Is there an official rule?
Hope you know what I mean, sorry for my English, I am from Germany!

heads up should be alright. my guess is he flopped TPTK.

Like all rules, this can be room specific. But in most rooms, showing your card or cards, or talking about your hand, is acceptable if 1) it is a cash game (not a tournament), and 2) the hand is headsup. In the situation you described, most rooms I have played in would not have an issue.

Willkommen,

Du sollst den Regeln lesen, es ist wahrscheinlich möglich, weil est gibt nür zwei Spieler, aber ein anderen Kasino vielleicht anderen Regeln haben

Thanks for your answers! :-)

For those of you who aren't familiar with German, that answer was so kind and helpful it seemed totally out of character for sixfour.

FYP

Your German is better than my English..

Contrary to other posters, most of the rooms I have played in showing cards is not allowed, but doing so would only result in a warning. One room I've played in they will kill your hand.

Room dependent, as is with most issues. I personally don't see why anyone would oppose doing it because it only gives the other player more information. I guess some people that got fooled (but probably were going to make the wrong decision anyways) complained in the rooms where they don't allow it.

Actually my room is totally insane. I rarely play donkaments but after a long time I played and facing a shove closing the action I said something along the lines of "I have the same hand I had last hand" and the dealer was moving in to muck my hand. Of course I always protect it (protect by holding on to it, not putting a chip on it) so floor came and they said the rule was you can't tell the truth about your hand and they go straight to killing hands. How they knew I wasn't lying was beyond me but just saying be aware of any idiotic rules before playing.