The electronic cigarette has been suggested as a safer alternative to the conventional tobacco cigarette. However, some vaping products have been shown to have cardiovascular effects, although this remains controversial. Several clinical studies have identified a possible alteration of endothelial function due to exposure to e-cigarette aerosols. However, the underlying biological mechanisms responsible for this observation in humans are still unclear. Thus, the development of preclinical mechanistic studies seems necessary. The aim of this review is, therefore, to provide a comprehensive overview of preclinical studies addressing the question of how e-cigarettes may cause endothelial dysfunction, a predictive marker of cardiovascular events. 53 papers were included in the analysis. We analyzed these papers qualitatively and quantitatively and discussed their limitations. We found that while 30% of in vitro studies showed no effect of e-cigarette aerosols on endothelial cells 26% showed variable effects, and 44% showed a significant adverse effect on endothelial function. In vivo studies were more consistent, with the vast majority (96%) reporting negative effects of e-cigarettes on endothelial function. We concluded that e-cigarettes should not be considered harmless in terms of cardiovascular effects, as they may impair endothelial function through various mechanisms such as oxidative stress and inflammation. However, more studies with standardized and optimized designs are still needed to distinguish the role of nicotine, which is known to affect the cardiovascular system, from that of other components in e-cigarette aerosol.