A catheter has an inflatable assembly at its distalportion, including a containment chamber, an axial core and aplurality of longitudinally oriented partitions extendingfrom the axial core to the wall of the chamber to divide thecontainment chamber into at least four inflatable sectors.Hydraulic valves are connected to respective sectors toenable selective inflation of the sectors by a fluid when thevalves are connected to a source of the fluid, and at leastone surface electrode is mounted on each of the sectors. Whenintroduced into a heart chamber and diametrically opposedsectors are inflated the assembly is stably fixed against thewalls of the heart chamber and readings can be obtained fromthe surface electrodes of the inflated sectors.
