Isoparametric 8-node hexahedral Finite Elements (FEs) are widely used for the simulation of 3D structural problems, providing excellent results in the case of regular meshes. However, they fail when the Jacobian determinant of the geometry mapping vanishes inside the element. In the presence of complex geometries, creating a mesh of only mildly distorted brick elements can be a very time consuming task, or even impossible in some cases. In contrast, 3D Virtual Elements (VEs) [1] are very robust with respect to extreme element distortion, but their geometry has been so far mainly limited to polyhedral elements with planar faces. To alleviate the meshing problem, a new 8-node, order 1, self-stabilized hexahedral VE with curved faces, named \emph{virtual brick}, is proposed to allow for the integration of highly distorted VEs in meshes of regularly shaped FE isoparametric bricks, thus significantly reducing the meshing effort. The virtual brick is developed within the framework of a Hu-Washizu mixed variational formulation [2] for large strain hyperelastic problems. Besides being fully compatible with regular 8-node isoparametric FEs, the integrals on the element faces and in the volume of the proposed virtual brick can be computed using the standard Gauss quadrature rules of the isoparametric FE, also in the degenerate case, as long as the virtual brick faces do not intersect with each other. This is a very useful property, especially in the nonlinear case, as the one considered in this work. Several numerical tests are conducted to show that when a FE brick becomes too distorted for being considered to be an isoparametric element, it can be easily replaced by a virtual brick, while continuing to use isoparametric FEs for the remaining regular part of the mesh, without compromising the simulation accuracy or the convergence order of the simulation.