Recent emerging nanotechnologies allow for demonstrating heterogeneous nanoporous structures. However, studies on the roles of heterogeneous nanostructures on adsorption and capillary transition are rare. Here, we examine the adsorption and capillary transition in heterogeneous structures using Ar-filled Pt-based nanogaps with one surface having nanoposts. Results from Grand Canonical Monte Carlo (GCMC) simulation show that the capillary transition pressure decreases at given temperature (or it increases at given pressure) by increasing the nanopost height, l(z), decreasing the distance, l(p), between nanoposts, and increasing the solid-fluid interatomic potential, epsilon(sf). A bimodal adsorption-capillary transition is observed when the two characteristic sizes of nanoposts and nanogaps are similar, which is caused by the capillary transition among nanoposts followed by another capillary transition across the nanogap. The second capillary transition pressure decreases with increasing nanopost height. The presence of nanoposts on one surface reduces the hysteresis compared to both bare surfaces, and no apparent bimodal capillary transition is observed in the desorption curve. Obtained results provide new insights into the role of locally heterogeneous structures in adsorption and capillary transition and the role of surface interaction in changing the adsorption isotherm.