A method is provided, including inserting a catheter into a right atrium of a heart of the subject. A distal portion of the catheter is advanced toward a fossa ovalis of the heart. A flexible longitudinal member is deployed from the catheter, such that a deployed portion of the flexible longitudinal member is loop-shaped. The fossa ovalis is contacted with the deployed portion of the flexible longitudinal member. A needle is deployed from the catheter. A distal end of the needle is brought in contact with a site on a surface of an interatrial septum of the heart outside the fossa ovalis. A hole is formed through the interatrial septum at the site with the needle. The deployed portion of the flexible longitudinal member is withdrawn toward the catheter.