The year 2004 brought a number of important events in cryotherapy. CryoCath Technologies, Inc. remained the only company with FDA-approved products for clinical use in cryoablation of arrhythmias. In 2004, the FDA approved the use of the Freezor Max catheter for use in the US. Both the Freezor Max and the Freezor Xtra catheters have been in long-term use in Europe, where the Freezor Max is used extensively for the ablation of atrial flutter. Not only does this 8 mm tip catheter form lesions of enough magnitude to cause interruption of conduction through the cavo-tricuspid isthmus, but it does so with absolute lack of pain. This allows for flutter ablation with minimal, if any, conscious sedation. At the conclusion of 2004, the US market now has availability of the Surgifrost surgical catheters and the Freezor catheters for FDA-approved clinical use. In addition, over 100 EP cryoablation systems have been sold in the US since approval. The use of catheter cryoablation for treatment of AV nodal reentry was FDA approved last year. In July of this year, the pivotal study leading to approval (FROSTY) was published in the journal Heart Rhythm. This spurred on the increase in the use of this technique for ablation of AVNRT. Multiple other papers were published on the use of cryoablation for treatment of arrhythmias of perinodal origin in adults and in children. The first randomized trial of radiofrequency (RF) versus cryoablation in AVNRT was published in 2004. It confirmed the increased safety of cryoablation while maintaining similar procedural times and outcomes. The authors concluded that the small increase in recurrence rates with cryoablation was more than offset by the benefits of its safety. In adults, the popularity of the technique continued to increase this year as the word spread amongst electrophysiologists on the safety advantages of cryoablation over RF. Cryoablation has become the preferred approach to ablation of arrhythmias of perinodal origin in the pediatric population in which the room for error is even smaller than in adults. Novel uses of the technology in 2004 included the first few reports of cryoablation in the pericardial space in humans. Papers on the safety and transmurality of lesions delivered epicardially in both animal models and in human clinical use were reported. Of importance, this technique is starting to be looked at for the treatment of atrial fibrillation (AF) by epicardial catheter-based approach. The surgical use of cryoablation for pulmonary venous encircling using the SurgiFrost continued to increase. Initial animal work using the cryo-clamp for AF treatment in the beating heart was reported this year. Similarly, focal and linear lesions for treatment of VT were explored and reported in animals. In both these cases, transmural lesions with discrete borders were created. Atrial fibrillation remains the holy grail of electrophysiology. Reports in 2004 of serious complications and deaths caused by aggressive LA radiofrequency ablation have tempered the enthusiasm for the more intense (and ostensibly more successful) versions of this procedure. CryoCath had ongoing protocols in Europe and in the US of pulmonary vein isolation using the Arctic Circler catheter. The Arctic Circler balloon trials are ongoing in Europe and are starting feasibility assessment in the US. No data are currently published on these trials, but the rumor is that they appear promising to date. At the close of 2004, there is no definitive approach for the catheter treatment of AF that balances safety and effectiveness. The evolving trials, clinical experience, and risks demonstrated with RF are renewing interest in pulmonary vein isolation. The Arctic Circler balloon holds the promise of being the safest of the effective techniques for this approach. The year 2005 should provide us with this answer. Cryoablation has become part of the clinicians armamentarium in the treatment of arrhythmias. In short, the year 2004 solidified the position of cryoablation as the safest treatment for AV nodal reentrant tachycardia and arrhythmias of perinodal origin. This year opened the doors for flutter cryoablation in the US, as has been reported by our European colleagues. Glimpses of what cryoablation can do for pulmonary vein isolation were seen in small clinical reports of Freezor used for focal PV isolation. Freezor Xtra and Freezor Max should allow further exploration of this use. On the horizon, Arctic Circler, Arctic Circler Balloon and Cryo-Clamp will be tools hopefully available for clinical research in the treatment of atrial fibrillation in the US next year.