Apparatus and methods are described, including apparatus for puncturing a fossa ovalis of a heart. The apparatus comprises a catheter shaped to define a catheter lumen. A puncturing element is slidably disposed within the catheter lumen and configured to (a) be deployed from a distal portion of the catheter, and (b) puncture the fossa ovalis. A balloon is configured to be deployed from the distal portion of the catheter, be radially expanded, and upon being deployed and expanded, facilitate positioning of the puncturing element, by contacting at least a portion of the fossa ovalis. Other applications are also described.