A deflectable tip catheter that is used in combination with a guidewire for delivery of an ablation element to target areas of a patient's vasculature. The deflectable tip catheter has a handle portion, an elongated shaft and a deflectable tip portion. A guidewire lumen extends through the elongated shaft and deflectable tip portion. A guidewire passes through the guidewire lumen and exits from a port in the distal end of the deflectable tip portion. The deflectable tip of the catheter is deflected by manipulation of the handle portion to direct the advancement of the guidewire as the guidewire is advanced out of the distal port. By using the deflectable tip portion to direct the advancement of the guidewire, the physician's ability to navigate sharp angles is greatly improved. The deflectable tip catheter is particularly suitable for delivering an ablation element to a pulmonary vein or pulmonary vein branch for performing circumferential ultrasound vein ablation to treat atrial fibrillation.