A cardiac treatment system of the subject technology provides access across an interatrial septum of a patient. Such a treatment system can include a catheter having an ablation treatment device on an outer surface of a distal region thereof. A needle is provided at least partially within a lumen of the catheter. A control unit is operatively connected to the ablation treatment device for ablation of a portion of a septum by RF ablation. A distal end of a catheter is provided to the septum (e.g., at the fossa ovalis) of the patient while a distal tip of the needle is within the lumen and proximal to the distal end of the catheter. The distal tip of the needle punctures and crosses the septum, and a portion of the septum is ablated with an ablation treatment device aligned with the septum by guidance from the needle.
