Heat exchanger , comprising: a plurality of heat exchange plaques and a plurality of plates stacked one by one on each other along a stacking direction (Y-Y) to define, in the space comprised between two adjacent plaques , coolant passage channels and hot passage channels to be cooled arranged perpendicularly to the stacking direction (Y-Y) and configured to be crossed by a coolant fluid (C) and by a hot fluid (H) to be cooled, respectively, wherein each plaque has a coolant fluid inlet opening (IC ), a coolant fluid outlet opening (OC ), a hot fluid inlet opening (IH ) and a hot fluid outlet opening(OH ) collimated with the respective openings of additional plaques to define coolant fluid inlet/outlet ducts of the (IC, OC) and hot fluid inlet/outlet ducts (IH, OH) for the fluids (C, H), wherein the coolant fluid inlet/outlet ducts (IC, OC) and the coolant fluid inlet openings (IC ) and the coolant fluid outlet openings (OC ) are in communication with the coolant passage channel , and wherein the hot fluid inlet/outlet ducts (IH, OH) and the hot fluid inlet openings (IH ) and the coolant fluid outlet openings (OH ) are in communication with the coolant passage channel , characterized by the fact that each plate is modular and comprises: a first lateral plate configured to be positioned at the point where the hot fluid inlet opening (IH ) and the coolant fluid outlet opening (OC ) are located, and a second lateral plate configured to be positioned at the point where the coolant fluid inlet opening (IC ) and the hot fluid inlet opening (OH ) are located and by the fact that said lateral plates are connected to each other by means of respective connecting bars . a plurality of heat exchange plaques and a plurality of plates stacked one by one on each other along a stacking direction (Y-Y) to define, in the space comprised between two adjacent plaques , coolant passage channels and hot passage channels to be cooled arranged perpendicularly to the stacking direction (Y-Y) and configured to be crossed by a coolant fluid (C) and by a hot fluid (H) to be cooled, respectively, wherein each plaque has a coolant fluid inlet opening (IC ), a coolant fluid outlet opening (OC ), a hot fluid inlet opening (IH ) and a hot fluid outlet opening(OH ) collimated with the respective openings of additional plaques to define coolant fluid inlet/outlet ducts of the (IC, OC) and hot fluid inlet/outlet ducts (IH, OH) for the fluids (C, H), wherein the coolant fluid inlet/outlet ducts (IC, OC) and the coolant fluid inlet openings (IC ) and the coolant fluid outlet openings (OC ) are in communication with the coolant passage channel , and wherein the hot fluid inlet/outlet ducts (IH, OH) and the hot fluid inlet openings (IH ) and the coolant fluid outlet openings (OH ) are in communication with the coolant passage channel , characterized by the fact that each plate is modular and comprises: a first lateral plate configured to be positioned at the point where the hot fluid inlet opening (IH ) and the coolant fluid outlet opening (OC ) are located, and a second lateral plate configured to be positioned at the point where the coolant fluid inlet opening (IC ) and the hot fluid inlet opening (OH ) are located and by the fact that said lateral plates are connected to each other by means of respective connecting bars . a first lateral plate configured to be positioned at the point where the hot fluid inlet opening (IH ) and the coolant fluid outlet opening (OC ) are located, and a second lateral plate configured to be positioned at the point where the coolant fluid inlet opening (IC ) and the hot fluid inlet opening (OH ) are located and by the fact that said lateral plates are connected to each other by means of respective connecting bars . <EOS>