Abstract: A steerable or deflectable distal tip of a cardiac instrument is provided by creating a differential tension in a distal portion, causing the distal portion either to curve if originally straight, or to straighten if originally curved. The differential tension can be created by a pull or push wire disposed in a longitudinal lumen of the instrument, which wire is attached at its distal end to the instrument. In another embodiment, the differential tension is created by thermoelectrically heated by metallic strip which is disposed within a lumen within the instrument in the form of a stylet. In another embodiment, the stylet is deformed by virtue of differential tension being applied between a pair of strips comprising the stylet.