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Atrial fibrillation (AF) affects 1% of the population and is associated with stroke and death. AF is often triggered by foci and reentrant pathways located near the pulmonary vein. Clinical studies show that circumferential pulmonary vein ablation destroys these electrical pathways, thereby eliminating AF (Pappone, C. et al., 2003). Currently, radiofrequency (RF) electrodes are used for such treatment. However, these procedures take over 7 hours and have <80% long term success. RF burn patterns often have discontinuities, which means that electrical pathways are still intact to trigger AF. Balloon and lasso catheters have been suggested to create a continuous circumferential burn, but are not successful because it can be difficult for the catheters to form good contacts with the tissue. Intravascular ultrasound arrays can be precisely electronically steered, making it easier to produce continuous burn patterns. The same array could also image the region of interest to position the burn correctly. While large external ultrasound transducers have been used ex vivo to ablate cardiac tissue (Strickberger, A.S. et al., 1999), external ultrasound for heart procedures is difficult because air in the lungs deflects much of the ultrasound. We propose the use of an intravascular linear ultrasound array placed at the end of a catheter. We present calculations, designs, and a proof of concept experiment demonstrating the feasibility of such an intravascular ablation system.