  Given a 4d N=2 SUSY gauge theory, one can construct the Seiberg-Witten
prepotentional, which involves a sum over instantons. Integrals over instanton
moduli spaces require regularisation. For UV-finite theories the AGT conjecture
favours particular, Nekrasov's way of regularization. It implies that
Nekrasov's partition function equals conformal blocks in 2d theories with
W_{N_c} chiral algebra. For $N_c=2$ and one adjoint multiplet it coincides with
a torus 1-point Virasoro conformal block. We check the AGT relation between
conformal dimension and adjoint multiplet's mass in this case and investigate
the limit of the conformal block, which corresponds to the large mass limit of
the 4d theory e.i. the asymptotically free 4d N=2 supersymmetric Yang-Mills
theory. Though technically more involved, the limit is the same as in the case
of fundamental multiplets, and this provides one more non-trivial check of AGT
conjecture.
