Oracle Text

At the beginning of the end step, if no creatures are on the battlefield, sacrifice Pyrohemia.

R: Pyrohemia deals 1 damage to each creature and each player.

Card Rulings

10/4/2004 Each activation is considered a new damage effect. An activation can only be 1 point of damage.
2/1/2007 This is the timeshifted version of Pestilence.
6/1/2011 Note that “until end of turn” effects wear off after “at the beginning of the end step” triggered abilities, so an artifact that animates until end of turn can keep this on the battlefield.
6/1/2011 It will stay on the battlefield if there is a creature that is put into the graveyard during the end step. This is because this ability will not trigger at all if there is at least one creature on the battlefield as the end step begins.