7 Pa. Code § 193.4
(i) In the event any horse or horses in the first half of the Daily Double should be excused by the racing officials after the horses shall have left the paddock for the post, or after the betting on the Daily Double has been closed, or should any horse or horses in the first half of the Daily Double be prevented from racing because of failure of the starting gate to open, the money wagered on any horse or horses so excused or prevented from racing shall be deducted from the Daily Double Pool and refunded to the purchaser or purchasers of tickets on the horse or horses so excused or prevented from racing.
(k) In case the second half of the Daily Double is not raced due to rain, or for any other cause, the entire pool shall be apportioned and paid, less commission, to the holders of tickets on the winner of the first race of the Daily Double.