In someone who is not accustomed to it, exposure to nicotine, whether through the lungs (smoking), mouth (snuff, nicotine gum, and chewing tobacco), or skin (nicotine patches), has three main effects on the heart:
- It increases the heart rate
- It causes the heart muscle cells to squeeze harder with each beat
- It causes blood vessels in the heart to constrict to a smaller diameter
At the same time, nicotine causes blood vessels in the body to constrict as well. All of these nicotine effects basically stress the heart, making it work harder than it has to at the time. The constricted heart blood vessels decrease the amount of blood flow the heart can receive. For these reasons, a very large, sudden dose of nicotine could bring on a heart attack, irregular heart rhythm or cardiac arrest.
All of these effects are temporary, however, because a person's body quickly becomes tolerant to the effects of nicotine; this is why nicotine is one of the most highly addictive substances known. Because of this tolerance to nicotine, for someone who chews tobacco regularly, the long-term heart effects are probably minimal. On the other hand, cigarette smoke contains other chemicals that contribute to atherosclerosis and the more rapid development of heart disease (heart attacks) seen in smokers. Our bodies cannot adapt to this effect.
Additionally, all tobacco products contain tar and related compounds that do not appear to affect the heart, but markedly increase the risk of cancer - of the mouth, throat, and stomach in those who chew, and in just about every organ for those who smoke.