Arrhythmias are a major cause of death and disability worldwide and their prevalence is expected to rise with the aging of the population. Recent technological advances have led to the development of new treatments based on radio-frequency (RF) catheter ablation to treat and even cure these conditions. However, challenges in treatment persist. RF ablation is currently performed via direct contact with the endocardium, limiting the depth of tissue injury unless high temperatures are used, which lead to higher risks of clot formation. Another major limitation is the lack of combined imaging modality for real-time monitoring of the treatment and for accurate assessment of the lesion extent. Our objective is to construct an ultrasound-based intra-cardiac ultrasound therapy/imaging system that can perform ablation using high-intensity focused ultrasound (HIFU) and can monitor the size and temperature of the ablation lesion using shear wave imaging (SWI). The specific aims of are 1) to develop an intra-cardiac hybrid system to perform HIFU, real-time temperature and lesion size monitoring using SWI, 2) Validate and optimize the imaging/therapy system in an animal model and 3) Demonstrate the feasibility of real-time RF ablation monitoring in patients using SWI. This project is tailored to facilitate the transfer of knowledge of the experienced researcher in imaging the with ultrasound at very high frame-rate the electromechanical properties of the heart. Upon completion, this project will result in the development of an intra-cardiac ultrasound system that allows performing non-contact ablation transmurally while monitoring the lesion site growth and temperature in real time. The capability of ablating at any location in the thickness of the myocardium while simultaneously assess the size of the lesion, has the potential to accelerate procedures, reduce the risks, and, provide a new approach to assess the success of the ablation.