Evidence suggests that traffic-related pollutants play a role in the observed associations between air pollution and adverse cardiovascular health effects. The contribution of traffic to individual exposures is difficult to quantify in traditional epidemiological studies, however, and researchers have employed various approaches in attempt to isolate its effects. Many investigators have employed ambient measurements such as nitrogen oxides, carbon monoxide, or black carbon as surrogates for traffic in studying associations with health outcomes. Source-apportionment techniques also have been used in a few studies to identify associations with the mixture of pollutants from specific origins, including traffic. In other studies, estimates of traffic near a person's home have predicted cardiovascular endpoints, and local traffic levels have modified the effect of regional air pollution. More recently, studies have linked changes in cardiovascular health to time spent in traffic. In this article, we review the epidemiological evidence regarding the impact of traffic-related pollution on cardiovascular diseases and examine the different techniques used to examine this important research question. We conclude with a discussion of the future directions being used in ongoing epidemiological studies to identify the cardiovascular health impacts of traffic.