Usually, the procedure is simple and straightforward and complete heart block can be achieved without any difficulty. However, this "simple" procedure can sometimes prove to be a most difficult case. The most common reason for failure to achieve complete heart block is the inability to localize the compact AV node using the His signal with standard intracardiac electrograms. As these patients come to the laboratory in AF, the His signal may be obscured by AF waves. In some patients with a deeper intramyocardial location of the His bundle and compact AV node it becomes necessary to produce deeper ablation lesions using an irrigated catheter to achieve block.