Smart watches are growing in popularity, with about one-in-five Americans reporting daily use of a smart watch or fitness tracker. Smart watches continue to gain functionality as technology improves, and have established their utility in several applications of physiological tracking including detection of atrial fibrillation, a common arrhythmia. Because they serve as a substitute for a typical wrist watch and have potentially lifesaving health and fitness features, smart watches present a unique opportunity to monitor and objectively track cardiac rhythm and sleep patterns. This current review seeks to explore the potential benefits and limits of smart watches in select cardiac applications, namely detecting arrhythmias and measuring heart rate variability (HRV). Because sleep quality and quantity often have an impact on cardiovascular systems, we also discuss smart watch sleep-cycle tracking functions.