Abstract: Objective: The purpose of the study is to evaluate the effect of pulmonary vein angiogram (PVA) and spike potential (PSP) mapping guided ultrasound ablation in the pulmonary vein ostium (PVO) to treat focal atrial fibrillation (Af).Methods: The target PVO of enrolled patient with paroxysmal Af was 1.clear and stable PSP，2.earliest APB orientation，3.PSP driven or triggered Af.An ultrasound balloon catheter was inserted through atrial septum to ablate target PVO with the parameters of temperature ≥50℃ and time 60～120s.The end points were PSP disappeared or its amplitude decreased more than 80%，complete conduction block from PVO to the left atrium and actual ablation temperature ≥50℃ for more than 60s.Results: Total 24 PVOs of 9pts were ablated.Each PVO was ablated (4.3±1.5) times with actual temperature of (57.2±3.6) ℃ and duration of (96.8±12.5)s.The PSP of 12 PVOs disappeared and the amplitude of others were decreased more than 80%.There were no complications.All pts had Af recurred with in (48.3±11.7) hours after ablation.Af was decreased from (5.7±3.9) to (3.4±2.3) per week in follow-up of 11.8±7.5month (P<0.05).Conclusions: 1.The end point of APB and PSP disappearance，actual temperature ≥50℃ can not predict immediate and long-term ablation effect of focal Af.2.Late remodeling effect of ablated PVO may be one factor to reduce Af attack.3.The method of PVA and PSP mapping guided ultrasound ablation in PVO may be not a radical care to focal Af.