Catheters, systems, and methods are provided for performing medical procedures, such as tissue ablation, adjacent the ostia of anatomical vessels, such as pulmonary veins. The catheter comprises an elongated flexible catheter body, which includes a proximal shaft portion and a distal shaft portion, and a tracking element carried by the distal shaft portion. The proximal section is pre-shaped to form a curve having an apex sized to be inserted into the vessel ostium, and a distal section configured to contact the adjacent tissue when the curve apex is inserted within the vessel ostium. The method may comprise inserting the curve apex into the vessel ostium to place the distal section in contact with a first tissue site adjacent the vessel ostium, and determining a location of the tracking element(s) within a coordinate system while the distal section is in contact with the first tissue site.