Abstract Body (Do not enter title and authors here): Background: Coil-less ultrasonic vaping devices like Surge use an ultrasonic chip that vibrates at several million Hz, aerosolizing the e-liquid. They are advertised as emitting significantly lower levels of toxins than coiled e-cigs by heating to lower temperatures that produce fewer chemical breakdown products. We tested the hypothesis that ultrasonic e-cigs cause less adverse cardiac effects than coiled e-cigs. Methods: We exposed 3 groups of conscious Sprague Dawley rats (n=8/group) to aerosol from JUUL (Virginia Tobacco 5% nicotine), Surge (Rich Tobacco 18 mg/ml nicotine), or air. Pulsatile exposure consisted of 10 consecutive cycles, each consisting of 2s exposure to aerosol followed by 28s of clean air, over 5 min, for 9 weeks using a Gram Research universal vaping machine. Hearts were then isolated, sectioned, and stained for left and right ventricular fibrosis with Sirius Red. Temperature profiles for the Surge ultrasonic vaping device were obtained at the California Department of Public Health (CDPH) via a single point thermocouple probe. Results: Temperature profiles of Surge during one session of aerosol production (with airflow) showed temperatures not exceeding 132 degrees Celsius. (We previously reported that the USONICIG Zip ultrasonic vaping device with air flow heated to ~77 degrees Celsius; reported temperatures of coiled e-cigs are up to 300 degrees Celsius.) Fibrosis was significantly increased in the JUUL group compared to air (p=0.04). Mean fibrosis in the Surge group was comparable to that in the JUUL group (p=0.84) and was higher than air fibrosis but did not reach significance (p=0.15), potentially due to high variability of Surge values. Conclusion: Temperature profiles of ultrasonic vaping devices are substantially lower than those of coiled vaping devices, with Surge being warmer than USONICIG Zip under airflow conditions. Despite lower temperatures, ultrasonic vaping devices cause a comparable level of cardiac fibrosis to conventional coiled vaping devices. Therefore, Surge does not avoid the increase in cardiac fibrosis that we have reported for coiled e-cigs and for smoke from tobacco or marijuana.