Smoking is a major independent risk factor for cardiovascular diseases (CVD), and the amount of smoking is an independent risk factor for mortality in patients with coronary atherosclerosis. The total amount of cigarette smoking is significantly associated with coronary artery disease and coronary artery stenosis. There is also evidence showing that either active or passive smoking can constitute a risk factor for cardiovascular disease. Passive smoking increases the risk of CVD by 70% to 80%, and this result is similar to active smoking. The relationship between smoking and cardiovascular disease risk has been confirmed, but the exact mechanism is not clear. The mechanism of atherosclerosis induced by smoking may be related to endothelial cell injury and elevated levels of nitric oxide in the blood. Inflammatory response plays an important role in the occurrence and development of atherosclerosis induced by smoking. It was found that the number of inflammatory cells (such as neutrophils and monocytes) increased significantly in the blood of smokers . Nicotine, as the main harmful component in tobacco, plays an important role in the occurrence and development of atherosclerosis . Although the e-liquid has removed tar and other harmful ingredients, more work needs to be done to evaluate its safety due to the existence of nicotine and other potential hazards such as aerosol particles and different flavor additives in e-liquid.(1)The harm of nicotine: smoking has become an independent risk factor for the formation of atherosclerosis, and the addictiveness of nicotine is known to all. Nicotine induces the release of catecholamine and cortisol, and causes hemodynamic changes (increase in heart rate, rise in blood pressure, and the vasoconstriction) and adverse effects on blood lipids (leading to activation of adenylate cyclase in adipose tissue and decomposition of triglycerides. The study found that the total lipid composition of the rats exposed to E-cigarettes smoke increased significantly, the content of saturated fatty acids increased significantly, while the content of unsaturated fatty acids decreased significantly), as well as the induction of insulin resistance . Nicotine can also cause endothelial dysfunction, inhibit apoptosis, and enhance angiogenesis. This effect raises concerns with regard to nicotine promoting cancer development and accelerating atherosclerosis . Researchers at Danderyd Hospital in Sweden have found that inhaling E-cigarettes only 10 times can cause signs of damage to the blood vessels. Subsequently, they further studied the effects on healthy people of inhaling E-cigarettes 30 times. Magnus Rudbeck, a doctor at Danderyd Hospital who participated in the study, believes that E-cigarette users have poor vascular elasticity, and the poor vascular elasticity may lead to heart disease and stroke. Researchers believe that the nicotine in E-cigarettes may lead to poor vascular elasticity . The study of Flouris, A.D. et al. found that white blood cell count increased after smoking E-cigarettes, which reflected the inflammatory process of acute cardiovascular events . The health status of E-cigarette users was analyzed. It was found that, compared with non-smokers, the former had an enhancement in cardiac sympathetic nerve excitability, and they were more prone to oxidative stress reactions. Professor Choupo Perk from European Society of Cardiology explained that the stimulation of atomized nicotine on sympathetic nerves can cause irregular beating of the heart and elevated blood pressure, and may cause long-term harmful effects on the growth of the vascular wall . Vlachopoulos, C. et al. investigated cardiovascular risk factors among 24 young smokers in 4 different smoking scenarios, and used femoral artery to femoral pulse wave velocity (PWV) to assess aortic stiffness, finding that E-cigarette smoke increased young people’s arterial stiffness and blood pressure, and smoking E-cigarettes for over 30 min had an adverse effect on arterial stiffness that was similar to that of traditional cigarettes . The study of Battista, L. et al. also showed that nicotine inhalation vapors produced the same pathophysiological cardiovascular effects as traditional cigarettes . Farsalinos, K.E. et al. studied the acute effects of E-cigarette smoke on the cardiovascular system of exposed people, and the results showed that the cardiac output blood pressure of people exposed to E-cigarettes (11 mg/mL of nicotine content) increased slightly; when the heart of smokers contracted, cardiac output and heart rate were significantly increased. They also used the MTT test to authenticate that the atomized e-liquid has toxic effect on cultured myocardial cells .(2)The hazards of aerosol particles were also studied. Zhang, Y. et al. showed that 73~80% of the particles were in exhaled aerosols, while 7~18% of the particles were stored in the alveoli. It is estimated that 20~27% of the particles entered the circulatory system, which is equivalent to the proportion for traditional cigarette smoke . Moreover, the size distribution and amount of particles of E-cigarettes are similar to those of traditional cigarettes, and some E-cigarettes produce more particles than traditional cigarettes. Particles may cause lung and systemic inflammation, and increase the risk of cardiovascular disease, respiratory disease and death .