A slide valve for blocking a line conveying media includes a housing having a passage opening and a slider plate moveable within the housing at right angles to the passage opening. The slider plate can be displaced from an open position into a closed position blocking the passage opening tightly by a drive mechanism. A lateral seal is disposed in a respective groove in the housing above the passage opening on both sides of the slider plate at right angles to its direction of displacement. The inside and outside of the housing and the slider plate are provided with at least one layer forming a temperature barrier, and the lateral seal includes a high temperature-resistant layer or sealing compound. The risk of a leak into the atmosphere and/or in the passage during a fire or during extinguishing efforts is thus substantially reduced.