Usually there are 4-5 PVs in each person that bring blood form the different lobes of the lung into the LA. Typically the inside lining of the LA extends for 3-7 mm inside the PVs around the entire circumference as they connect (ostium; os) in the form of finger like projections. These projections are thought to be the sites that initiate AF. The procedure involves careful definition of the finger like projections between the LA and PV os using the circular mapping catheter (Lasso). The connections produce specific pattern of electrical recordings which are targeted using the ablation catheter that utilizes radio-frequency energy to create local burns at the point of contact with the inside of the heart. A successful burn destroys these finger-like projections which can be appreciated by loss of the characteristic electrical recordings which were seen pre-ablation. Using this technique, a series of radiofrequency ablation lesions are delivered around the circumference of PV, the end point being obliteration of all electrical recordings between the left atrium and the PV of interest (also called "Electrical Isolation" of PV from the rest of the LA). At this time the ablation procedure for AF involves electrical isolation of either those PVs that have been shown to be the sites from where AF starts (arrhythmogenic PV) or empirically isolating all the PVs that the patient has (typically 4-5). There is lack of data showing benefit of one technique over the other. Additionally, in order to create radiofrequency lesions or burns inside the heart, two different catheter technologies have been approved and are currently in use: 1) radiofrequency delivery using a standard 4-mm tip or 8-mm tip catheter, which creates burns at the point of catheter contact that are approximately 5 mm deep and 2) delivery of radiofrequency energy via saline irrigated cool tip catheter which is capable of creating deeper burns (5 - 10 mm). Once again, for electrical isolation of pulmonic veins in pts with AF, there is no data that proves the benefit of either catheter technology over the other.