E-cigarettes are not approved by the US Food and Drug Administration for smoking cessation. The limited research published to date has not proven that electronic cigarettes are effective smoking cessation aids. E-cigarettes are unregulated and that users cannot be sure what they are exposed to.
Cardiology article for E-cigarettes by the American Heart Association: (http://circ.ahajournals.org/content/129/19/e490.long)