Pennsylvania law treats the giving of an engagement ring as a conditional gift.  According to Pennsylvania courts, the giving of an engagement gift has an implied condition that the marriage must occur in order to vest title in the donee.  The mere acceptance of the marriage proposal is not the implied condition for the gift.  In Lindh v. Surman, the court held that the donor is entitled to return of the engagement ring even if the donor broke the engagement.[1]

[1] Lindh v. Surman, 560 Pa. 1 (Pa. 1999)