You can cast a spell as if it were a higher level spell than it actually is.
Benefit: A heightened spell has a higher spell level than normal. Unlike other metamagic feats, heighten spell actually increases the effective level of the spell that it modifies. All effects dependent on spell level are calculated according to the heightened level. The heightened spell is as difficult to prepare and cast as a spell of its effective level. For example, a cleric could prepare hold person as a 4th level spell (instead of a 2nd level spell), and it would in all ways be treated as a 4th level spell.