Arrhythmias are a major cause of morbidity and mortality, with more than 250,000 people dying suddenly each year in the United States. Most arrhythmias are acquired and result from damage to the heart or its electrical system by ischemia, infarction, cardiac surgery, viruses, and assorted non- cardiac diseases. Our ability to identify which patients are at the highest risk of sudden death is poor, with ejection fraction being the only major clinical tool available for risk stratification. In addition, internal cardioverter-defibrillator (ICD) placement is the only effective therapy for high risk patients. Thus, the identification for novel tools to study arrhythmias in-vivo and stratify arrhythmic risk would represent a major advance to cardiovascular care. With the funding from the Pioneer Award, we will develop two novel and revolutionary techniques to image electrical activity in the intact heart in-vivo. First, we will adapt the most common clinical imaging technique, two-dimensional doppler echocardiography, to detect electrical activity in real time. Second, we will develop a modified autologous stem cell implant to detect adrenergic activity in the heart. These techniques will be developed in-vitro, tested in-vivo using animal models, and applied to humans when possible. If successful, both techniques will increase our understanding of arrhythmia mechanisms, improve risk stratification in patients at risk for sudden death, and guide therapeutic interventions.