a cardiac arrhythmia mapping and ablation catheter has a main catheter that is provided with a mapping and ablation system attached to its distal end which includes an adjustable loop carrying an electrode array including a plurality of parallel - connected , separately operable mapping / ablation electrodes in conductive relation to the external environment and arranged in spaced serial relation along the loop . insulated conductors connect the electrodes electrically with an input / output device outside the catheter for mapping the electrical activity of the chamber wall contacted and ablating tissue as indicated . drawstring control wires are used to control the size , shape and deflection or posture of the loop . a distal extension may optionally be provided to adapt the loop specifically to addressing the tricuspid annulus . a fixed version is also disclosed .