Heighten Spell Feat Question

[clparis]

Here is the Heighten Spell (Metamagic).

Core Rule Book wrote:

Heighten Spell (Metamagic)

You can cast spells as if they were a higher level.
Benefit: A heightened spell has a higher spell level than normal (up to a maximum of 9th level). Unlike other metamagic feats, Heighten Spell actually increases the effective level of the spell that it modifies. All effects dependent on spell level (such as saving throw DCs and ability to penetrate a lesser globe of invulnerability) are calculated according to the heightened level. The heightened spell is as difficult to prepare and cast as a spell of its effective level.

My questions are how many spells does it apply to (I assume one) and can it be taken several times for different spells?

[bigkilla]

You only take the feat 1 time.

Every time you memorize spells for wizards and witches and clerics you can choose to apply the feat to the spell and it modifies the level of the spell.

Or if you are a spontaneous caster you apply it when you cast the spell and it modifies the spell from there.