Abstract. Let E be an elliptic curve over Q and A be another elliptic curve over a real quadratic number field. We construct a Q-motive of rank 8, together with a distinguished class in the associated Bloch-Kato Selmer group, using HirzebruchZagier cycles, that is, graphs of Hirzebruch-Zagier morphisms. We show that, under certain assumptions on E and A, the non-vanishing of the central critical value of the (twisted) triple product L-function attached to (E, A) implies that the dimension of the associated Bloch-Kato Selmer group of the motive is 0; and the non-vanishing of the distinguished class implies that the dimension of the associated Bloch-Kato Selmer group of the motive is 1. This can be viewed as the triple product version of Kolyvagin's work on bounding Selmer groups of a single elliptic curve using Heegner points.