High frequency alternating current electric fields block electrical waves in the heart. The top panel is a map of the electrical activity on the surface of the heart, and the bottom panel is the electrical activity at the site shown in the map. A stimulus elicits electrical waves from near the top of the heart. After one second, a high frequency electric field is applied (white background) and blocks the electrical waves. After another second, the field is turned off, and electrical waves again propagate without any lasting effects from the field. This video relates to a paper that appeared in the Sept. 28, 2011, issue of Science Translational Medicine, published by AAAS. The paper, by Dr. Hari Tandri of Johns Hopkins University in Baltimore, MD and colleagues, was titled, "Reversible Cardiac Conduction Block and Defibrillation with High-Frequency Electric Field."