Key design features include the angled tip, which facilitates passage across the interatrial opening to the left atrium. Once an adequate defect is created, the catheter can then be used to estimate the size of the opening. A single lumen wire wound catheter body allows for visualization under fluoroscopy. A stylet increases body stiffness and allows for temporary straightening of the tip angulation during insertion. The Miller catheter includes a plug for occluding the vein or percutaneous sheath to reduce venous leakage.