The aim of the career development and research strategies of this proposal are to build an independent clinician-scientist career focusing on: 1) reliable imaging of parameters that contribute to arrhythmia pathophysiology and ablation procedure outcome, 2) understanding how patient specific structural variations affect arrhythmia propagation and response to treatment, and 3) developing a cellular to organ system level understanding of arrhythmia pathophysiology, that will serve as a basis for future work. My background in clinical electrophysiology, imaging science, and computational modeling is well suited to the goal of improve arrhythmia treatment through individualized image guided therapy. My career development goals will be achieved through a combination of course work and mentored research at the Johns Hopkins University School of Medicine and Department of Biomedical Engineering. Johns Hopkins provides a stimulating research and clinical environment and has a long history of training leaders in patient-oriented research. The institution has a particular strength in studying the cellular to organ level aspects of cardiac electrophysiology and arrhythmia pathophysiology. The structured coursework portion of this career development program will include training in advanced topics in MRI research, image integrated computational modeling, clinical study design, and research ethics. The mentored research potion of this career development award will focus on cardiac magnetic resonance imaging (CMR) during arrhythmia. While many tachy-arrhythmias are curable by catheter ablation, some common conditions, in particular atrial fibrillation and ventricular tachycardia (VT), are sub-optimally managed by current medical and ablation treatments. Cardiac magnetic resonance imaging (CMR) is of increasing interest to cardiac electrophysiology because 1) CMR has the potential to visualize myocardial scar and fibrosis, which are important to VT and atrial fibrillation pathophysiology, and 2) CMR has the potential to visualize ablated tissue as well as gaps in intended regions of ablation. These gaps may not conduct acutely, so that the arrhythmia may not recur immediately after ablation, but the gaps can regain conduction over time. This recovery of conduction is likely a major mechanism for arrhythmia recurrence after ablation. The ability to visualize gaps with CMR, and eliminate those visualized gaps, would likely dramatically reduce the high incidence of VT and atrial fibrillation recurrence after ablation. Current high-resolution CMR techniques for imaging scar, fibrosis, and ablation lesions, however, are not reliable enough for routine clinical application. The proposed research will further develop techniques to perform more reliable high-resolution CMR during arrhythmia and will investigate related CMR applications of 1) predicting successful ablation sites by imaging regional wall motion during arrhythmia and 2) predicting ablation adequacy using arrhythmia resistant CMR thermography. The theme of this work is to provide more specific and individualized image guided therapy toward the goal of increasing the efficacy, speed, and safety of arrhythmia ablation procedures.