1. A treatment and/or diagnostic system for use in a chamber of a heart, the chamber containing blood, the system comprising: an articulatable catheter; an imaging assembly supported by the catheter, the imaging assembly configured to acquire a tissue surface image of a tissue surface region of the chamber while at least a portion of the blood is disposed in the chamber; at least one sensor configured to detect an electrical activity of the tissue surface; and a processor coupled to the imaging assembly and the at least one sensor so as to receive the detected electrical activity and tissue surface image, the processor configured to map the detected electrical activity and tissue surface image together.