Heroic Sacrifice is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Choose target creature you control. Until end of turn, all damage that would be dealt to you and creatures you control is dealt to the chosen creature instead (if it's still on the battlefield). When that creature dies this turn, put its counters on up to one target creature you control and draw a card.