Hydraulic stimulation of unconventional reservoirs, such as Vaca Muerta formation, is one of the key-factors to reach economically attractive productivity. It is therefore, of fundamental interest to understand and predict the hydraulic fracture behavior, which is affected by several factors, including the stress state, the stimulation protocol and the characteristics of the reservoir.One of the important aspects that can impact on the stimulation success, is the presence of mechanical heterogeneities in the reservoir due to vertical changes in the lithology. In Vaca Muerta formation, for example, different facies with variable content of organic matter, carbonates, volcanic deposits, among others, with diverse textures, coexist (Sagasti et al. 2013). They produce a distinct mechanical behavior to each facie. The contact surface of two facies with different mechanical properties are called interfaces, which, depending on their lithologies and origins, may have different characteristics.In this work we numerically study the effects of weak interfaces (planes with low cohesion and friction) in the propagation of the hydraulic fracture, in both, 2D and 3D. We also designed and performed laboratory tests to analyze the possibility of sliding of a weak interface due to the stimulation.