Abstract: Apparutus and methods are described for performing percutancous catheter-based interventional surgery. The apparatus comprises first and second devices that are located in adjacent body cavities, such as adjacent blood vessels, the first device being capable of transmitting a directional signal that can be received by the second device. The direction of the signal is correlated with the facility to direct therapy, such that improved accuracy in therapy placement is thereby achieved. Methods for treating patients utilising the means and apparatus are also provided.