if slitherin does there has to be for all the houses . maybe voldemort is related somehow to salazar so that is why he is the heir so maybe someone who shows a quality great of the house they are in will be the heir. they thought harry had to be the heir of slithein because he was suppose to be in slitherin because some of his qualities are those of a slitherin he is parseltoungue (Sp?) so he probably might even be the heir to griffindor becase he isalso brave . somebody do understand what i am saying right???? but if not it's ok