Masonry walls exhibit low tensile strength and high material heterogeneity, which makes them especially vulnerable against accidental loadings. There are a large number of studies, both experimentally and numerically, of the masonry behaviour under accidental loadings such as earthquakes. In this regard, the most relevant research focuses on (1) evaluating the shear strength of masonry with diagonal compression tests, (2) its behavior against in-plane cyclical loadings and (3) textile reinforced mortars TRM-based reinforcement techniques. However, there are very few studies that analyse the behavior of masonry under high temperature exposure, such as those that can occur in a fire. This paper describes the preliminary results of an experimental tests in which masonry panels (reinforced with TRM and unreinforced) have been tested in diagonal compression, previously damaged by the fire exposure. For this, masonry panels were subjected to different temperature levels, up to a maximum of 600 degrees C using an electric oven. In general, the results show that high temperatures causes a decrease in shear strength, as well as the transverse stiffness modulus. However, the walls reinforced with TRM based on carbon fiber were the ones that presented the best performance, since their mechanical properties were reduced by a smaller percentage.