Ablation catheters and systems include multiple inline chambers for containing and heating an ablative agent. The heating chamber includes one or more channels to increase the contact surface area of the ablative agent with the walls of the heating chamber to provide more efficient heating. Induction heating is used to heat a chamber and vaporize a fluid within by wrapping a coil about a ferromagnetic chamber and providing an alternating current to the coil. A magnetic field is created in the area surrounding the chamber which induces electric current flow in the chamber, heating the chamber and vaporizing the fluid inside. Positioning elements help maintain the device in the proper position with respect to the target tissue and also prevent the passage of ablative agent to normal tissues.