Electronic cigarette use (e-cigarettes) has surged in popularity over the last decade particularly among young adults. Despite perceptions of reduced harm compared to traditional tobacco cigarettes, studies suggests that e-cigarette use may have adverse impacts on cardiovascular health, comparable to those of tobacco smoking. Understanding the impact of vaping on brachial artery blood flow responses to exercise is crucial for evaluating its impact on endothelial function, a biomarker for cardiovascular disease. This study aims to investigate brachial artery blood flow and diameter responses to dynamic handgrip exercise (DHG) in a vaping group compared to a non-vaping control group. This study had ethical approval from the University of Bristol (17598) and conformed to the Declaration of Helsinki. Fourteen healthy, non-tobacco smokers were recruited. Six participants (4 males) were regular e-cigarette users (vaping group; defined as ≥5 days per week >6 months) and 8 (5 males) were non-users who have never used e-cigarettes or tobacco products (non-vaping control group). The vaping group were asked not to vape before attending the study visit. After a 2-min baseline, DHG was performed at 40% maximal voluntary contraction (MVC) for 4 minutes, at 20 contractions/minute, followed by a 2-min recovery period. Brachial artery blood flow and diameter were measured continuously using vascular ultrasound via a (12-Hz Doppler probe with an insonation angle of 60° over the brachial artery). Blood pressure (Finapres) and heart rate (3-lead ECG) were measured continuously throughout the protocol. Brachial artery diameter and mean blood flow were calculated via synchronised Doppler waveform envelope analysis, edge detection, and wall-tracking of high-resolution B-mode arterial ultrasound images. Absolute and change from baseline values were analysed over 30s increments. Brachial vascular conductance was calculated as flow (mL/min) / mean arterial pressure (mmHg). The change in brachial blood flow and conductance from rest to the final 30 seconds of handgrip exercise were compared using an unpaired t-test. Data are mean +/- SD. There were no differences in age (controls; 22 ± 1.5 years vs. vapers; 22 ± 1.4 years, P=0.4467) or body mass index (23.3±2.1 kg/m2 vs. 22.6±3.8 kg/m2, P=0.6284). There was no difference in the change in blood flow from rest to exercise between controls and vapers (∆359±176 ml/min vs. 291±201 mL/min, P=0.2448). However, there was a large effect of vaping on brachial vascular conductance, where controls had a larger change from rest to exercise vs. vapers (∆4.0±1.6 ml/min/mmHg vs 2.6±1.5 ml/min/mmHg, P=0.0544, Cohen’s d (effect size)=0.90). Vaping potentially impacts vasodilator response to exercise but needs further research.