Using specialized cardiac catheters for image acquisition, features of the heart are readily identifiable on an ultrasound image, based on a previously generated electrical activation map of the heart. The electrical activation map is automatically registered with the ultrasound image using information obtained from position sensors in the catheters. Features identifiable on the electrical activation map, presented as points, tags, design lines, and textual identification, are projected into the plane of the ultrasound fan and overlaid on the ultrasound image, thereby clarifying the features that are visible on the latter.