Cigarette smoking is more prevalent (50-70%) in persons living with HIV in the U.S. when compared with the general population and is linked to increased rates of heart disease, lung diseases and infections, and lung cancers. Because of their high levels of nicotine dependence, low quit rates, and familiarity with harm reduction, HIV-positive smokers may view the use of alternative nicotine delivery products, such as electronic cigarettes (ECs), as an attractive option for reducing and eventually stopping combustible cigarette use. However, little is known about the health effects of electronic cigarette use in HIV-positive smokers. Some studies have shown that electronic cigarette use was associated with increased confidence to quit smoking in the general population. The primary objectives of this project are to examine whether HIV-positive smokers, who are unwilling or unable to quit smoking, will substitute an electronic cigarette for regular cigarettes, and to examine whether there are any changes in heart and lung health in HIV-positive smokers who switch from regular cigarettes to electronic cigarettes.