Background: Despite a lack of empirical data, an unprecedented rise in electronic cigarettes (ECs) has been widely perceived as safe. Multiple studies support a causal link between tobacco cigarette (TC) use and a decline in cardiovascular (CV) health; however, there is a paucity of data with EC use. A study showed EC use decreased HRV in humans via increased sympathetic activation- a known mechanism predictive of CV disease from TC use. We aimed to develop a mouse model to determine if acute EC exposure modifies HRV in mice. Methods: Telemetry devices were implanted in the abdomen of 6 eight-week-old C57BL/6 mice to monitor ECG activity continuously. Mice underwent a 1-hr acclimation phase in exposure chambers followed by a 1-hour exposure to air (control). EC exposures consisted of two 15-min sessions (4-sec puff/26-sec air) to BluPlus® 2.4% nicotine (Classic Tobacco) with a 15-min period of aerosolized PBS added as a secondary control. For each exposure episode, a 45-min post-exposure event followed. Ponemah v6.20 software was used for HRV analysis of the time domain. A linear mixed-effects model with a robust estimator was used to determine the relationship between air vs. combined EC events and PBS (n = 1,109). R (Version R3.6.3) was utilized to test for statistical significance at α = 0.05. Results: EC exposures significantly decreased the standard deviation of NN intervals (SDNN) and root mean square of successive differences (RMSSD) by 5.00 and 9.34 units as compared to air exposures, suggesting reductions in total and short-term autonomic variability (Table 1). Both parameters increased in the post-EC periods as compared with the EC exposures. Conversely, PBS vs. air exposure showed a marked increase in SDNN and RMSSD. Conclusion: Short-term exposures to ECs decreased HRV in mice, consistent with similar results in human studies, suggesting that ECs could increase cardiovascular risk in an acute manner.