Despite recent progress in prevention of coronary heart disease, approximately 50% of the deaths from coronary artery disease continue to occur out of hospital, and many major cardiac events occur in individuals not previously known to be at risk. These facts create the need to identify the acute causes of myocardial infarction (MI) and sudden death, which has led to a rapid growth in interest over the last 15 years in the field of triggering research. Since initial observations that the incidence of MI onset was time and activity dependent with circadian, circaseptan, and circannual variation, triggering of MI by heavy exertion, sexual activity, anger, mental stress, cocaine and marijuana use, and exposure to air pollution has been demonstrated. Study of the pathophysiological changes produced by these triggers may provide novel therapeutic and preventive targets by a more thorough understanding of vulnerable plaque disruption and coronary thrombosis.