Enter the text here that is the new abstract information for your application. This section must be no longer than 30 lines of text. Alcohol is the most commonly consumed drug in the world. Atrial fibrillation (AF) is the most common arrhythmia. In the original R01, we conducted a randomized trial of intravenous alcohol versus placebo to demonstrate an acute change in atrial electrophysiology expected to render the atria more prone to fibrillate and demonstrated a near-term risk of AF associated with alcohol consumption in an observational, case-crossover, study of ambulatory patients. Those findings coupled with a recent randomized trial showing that abstinence reduces AF burden along with an NIH priority to study utilization of digital health to promote alcohol abstinence in these patients motivate our revised Aim 1. In Aim 1, we will employ human-centered design in collaboration with AF patients and experts in behavioral change, alcohol use, technology, and implementation research to construct a smartphone-based mobile application purpose-built to promote alcohol abstinence specifically in AF patients. We will leverage our Eureka Digital Research Platform, our previous research findings, and recent integrations with commercially available smart watch-detected AF episodes to craft a starting framework for this Digital Intervention, including 1. Messaging; 2. An individualized visualization of alcohol-AF relationships; and 3. Real-time abstinence encouragement triggered by geofencing of establishments that sell alcohol. The Digital Intervention will be compared to a control condition in a randomized trial, with outcomes of AF burden and durable abstinence measured by self-report and objective assessments. In Aim 2 of this revised submission, we also seek to fill an important gap remaining in the study of alcohol and AF: definitive, randomized controlled trial evidence that alcohol consumption immediately heightens the risk of a discrete AF episode. New preliminary data ramifies the continued import of such information to AF patients, evidence of such a causal relationship would bolster the utility of the proposed Digital Intervention in Aim 1, and simultaneous assessments of physiology will provide mechanistic information also of priority per a recent NIH statement. In Aim 2, ambulatory paroxysmal AF patients will be fit with a continuously recording ECG, a transdermal alcohol sensor, and a Fitbit and will then receive randomization instructions daily to abstain or not abstain from alcohol. We are powered to detect clinically meaningful associations among AF patients drinking within guideline-acceptable limits, making this especially pertinent to the great majority of individuals who consume alcohol. Aim 2 participants will receive an individualized visualization of AF episodes versus their randomization assignments, and, with subsequent encouragement to avoid alcohol, will then be evaluated for durable abstinence using the same methods as those...