There is provided heat transport apparatus comprising a closed tube having an evaporator and a condenser with the condenser being positioned above the evaporator during operation. The closed tube includes a heat transport medium which, during operation, is vaporized in the evaporator and condensed in the condenser, the resulting condensate being returned to the evaporator. A valve is positioned in the closed tube in the condenser region for controlling the condensate return. A pressure-expansion chamber is arranged within the closed tube and is connected to the valve for closing the same when the vapor pressure in the condenser exceeds a given value. A pressure-equalization duct forms part of the valve and provides communication between the evaporator and the condenser.