Abstract: An ablation device for cardiac tissue, especially for forming a circular lesion around a vessel orifice in the heart, comprises a steerable catheter that is provided in the region of its distal end with an abutment device for holding the distal end of the catheter on a cardiac vessel orifice; and a linear ablation applicator that is disposed distally or proximally relative to the abutment device of the catheter and can be brought from a straight passive position into a radially expanded, approximately circular-arc-type encircling ablation position.