Abstract: Devices and a method are provided to assist a surgeon in ablating conduction paths in tissue, such as a heart. A device can be configured to operate as a template that adheres to the tissue surface, and allows the surgeon to more easily sever the conduction path to form a lesion in a desired location. In particular, the template can be used to guide the surgeon's use of a surgical instrument along a desired ablation path. In some case, the template may incorporate hardware that structurally supports the instrument for travel along the ablation path. A surgical instrument such as an ablation probe, e.g., radio frequency, laser, ultrasonic, microwave, thermal, chemical, mechanical, or cryogenic ablation probe, may be used to sever the conduction paths. Measurements made substantially contemporaneously with the conduction path ablation operation may be used to evaluate whether the desired degree of ablation has been achieved.