The damages caused by earthquakes show an existing heritage characterized by a strong fragility of the infilled frames and connections usually without seismic details. The damage detection, has directed the post-earthquake structural repairs on buildings toward strengthening of nodes that are not confined, and especially toward the adoption of  prevent overturning systems of the infills. However, several studies show, that the infilled frames usually increase the resistance to horizontal actions for small strains preceding to the damage, by causing in some cases, the changing of the global behaviour and collapse mode of the structure. In the present work, some remarks on the seismic improvement of existing buildings are carried out, induced by the possibility of solidarize the masonry panel to the structural elements. A real case study, consisting of an existing building in reinforced concrete, shows the results obtained through the reinforcement of the infills, highlighting the differences from the behaviour of the structure before of the intervention (in both configurations with and without infills).