A microwave heater equipped with a microwave choke and suitable for heating one or more articles under vacuum. The microwave choke inhibits leakage of microwave energy between a door of the heater and a main vessel body of the heater without causing arcing at the choke, even at low pressures. In certain situations, the microwave choke can be configured with side-by-side choke cavities. In certain situations, the microwave choke can be removably coupled to the door and/or vessel body for easier fabrication, installation, and/or replacement.