A heat responsive trigger assembly for a fire protection sprinkler may include a first plate having a bottom face; a second plate including a top face engaging the bottom face; a thermally conductive member disposed between the top and bottom faces and extending beyond a perimeter of at least one of the first and second plates; and a heat fusible material securing the first and second plates in an engaged position. The first and second plates may disengage in response to the heat fusible material reaching a predetermined temperature, thereby allowing a fire suppressant to discharge from the sprinkler.