The transseptal technique allows left atrial access from the venous system for catheter ablation of left-sided arrhythmogenic substrates. Many physicians prefer the transseptal approach; others use it when a transaortic (retrograde) approach is contraindicated. The Mullin Sheath and Brockenbrough Needle are sterile, single-use products designed to allow access to the left atrium during electrophysiology procedures. The sterile Mullin sheath/dilator set serves as a conduit for the needle and electrophysiology.