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A two-dimensional cylindrical-coordinate (2-D-cyl) finite-difference (FD) time-domain code together with an explicit 2-D-cyl FD solution of the bioheat equation were used for studying a 2450-MHz cap-choke antenna designed for microwave cardiac ablation. Following validation based on results available in literature, the numerical tools were used to evaluate the performance of the catheter antenna embedded in a homogeneous dielectric phantom. The results highlight the ability of the cap-choke catheter antenna to produce high specific absorption rate (SAR) values near the tip and, in contrast, very low SAR values along the antenna length. The comparison of computed data with measurements shows a good agreement between numerical and experimental results. The numerical tools were subsequently applied to analyze the catheter antenna embedded in a two-layer heart model in order to evaluate the depth of induced lesions in a more realistic model of the operating condition. In particular, both the effect of the antenna position relative to the blood-muscle interface (simply touching or pressed inside the muscle) and the effect of blood velocity (taking into account over-leaflets and underneath-leaflets positions) were investigated. It is shown that a lesion depth of 5 mm in a heart region with low blood perfusion could be obtained with approximately 16 W of radiated power, applied for 60 s.