Source: Complete Arcane
When you use your magic, your mere presence can terrify those around you.
Prerequisite: Draconic Heritage.
Benefit: Whenever you cast an arcane spell, all opponents within 10 feet of you who have fewer Hit Dice than you become shaken for a number of rounds equal to the level of the spell you cast. The effect is negated by a Will save (DC 10 + level of the spell cast + your Cha modifier).
A successful save indicates that the opponent is immune to your draconic presence for 24 hours. This ability does not affect creatures with an Intelligence of 3 or lower or creatures that are already shaken, nor does it have any effect on dragons.