Abstract. Circadian clocks play a fundamental role in aligning physiological and behavioral processes to predictable changes in the daily environment. For decades, circadian signaling has been implicated in the development of cardiac arrhythmias and sudden cardiac death (SCD) in individuals with cardiovascular disease. However, numerous critical knowledge gaps persist regarding the connection between circadian clocks, circadian rhythms, and SCD. This research proposal addresses these knowledge gaps by investigating the molecular mechanisms underlying the circadian regulation of ion channel transcripts and proteins that impact arrhythmia susceptibility. Aim 1 will elucidate the molecular mechanisms responsible for the circadian regulation of cardiac ion channel genes essential for cardiac excitability. Through comprehensive promoter analyses utilizing real-time bioluminescence assays (LumiCycle), we will identify the conserved cis-regulatory element(s) essential for circadian activity. The identified cis-regulatory element(s) will be validated using Chromatin Immunoprecipitation and electrophoretic mobility shift assays. Aim 2 focuses on determining how circadian alignment and misalignment affect the transcription and translation of genes essential for normal cardiac electrophysiology. We will explore the impact of time-restricted feeding on the transcriptional and translational regulation of myocardial genes important for cardiac excitability by employing mRNA-seq and Ribo-seq technology. Aim 3 will determine the physiological implications of circadian alignment and misalignment on cardiac electrophysiology, autonomic regulation, and arrhythmia susceptibility. We will assess the impact of manipulating feeding-fasting cycles on cardiac electrophysiology and arrhythmia susceptibility utilizing an arrhythmogenic mouse model with impaired cardiac conduction and ventricular refractoriness (Scn5a+/-). We will also investigate how feeding-fasting cycles modulate the autonomic nervous system's regulation of cardiac electrophysiology using an inducible cardiomyocyte-specific Rrad knockout mouse model (iCSΔRrad). This interdisciplinary project lies at the interface between chronobiology and cardiac electrophysiology, and it will generate new knowledge to provide valuable insight into how circadian clocks and alignment impact the risk for cardiac arrhythmias. In addition, the results of this project are expected to identify novel chronotherapeutic strategies that can readily be adopted to mitigate arrhythmogenic risk in vulnerable populations.