A mapping catheter adapted for use in a heart chamber, has a distal mapping assembly (19) with a spiral ribbon that is radially expandable and contractable by longitudinal movement of an expander (22) so that electrodes (21) on the ribbon can contact heart wall at a plurality of locations simultaneously. The expander extends the length of the catheter between a control handle (16) and a distal end of the spiral ribbon. The expander can be controlled directly at its proximal end by a user or the expander can be responsive to a puller wire controlled by a user interface on the control handle. At least one shape-memory strut extends along the length of the spiral ribbon to flexibly support the spiral form.
