Downing, Stephen W., William R. Herzog, Jr., Michael C. McElroy, and Timothy B. Gilbert. 2002. “Feasibility of Off-Pump ASD Closure Using Real-Time 3-D Echocardiography”. The Heart Surgery Forum 5 (2):E096-E099. https://journal.hsforum.com/index.php/HSF/article/view/6167.