Your breath weapon is larger than normal.
Prerequisites: Con 13, breath weapon with recharge time expressed in rounds.
Benefit: The length of your breath weapon increases by 50% (round down to the nearest multiple of 5). For example, an old silver dragon breathing an enlarged cone of cold produces a 75-foot cone instead of a 50-foot cone. Cone-shaped breath weapons get wider when they get longer, but lineshaped breath weapons do not.
When you use this feat, add +1 to the number of rounds you must wait before using your breath weapon again.
Source: Draconomicon, page 70.