A large body of evidence indicates that a persistently high heart rate is associated with a significant risk for higher mortality and sudden death in individuals with a variety cardiovascu- lar disorders, as well as in the general population. Heart rates elevated beyond a certain threshold have been found to be a risk factor for mortality in patients with hypertension, in survivors of myocardial infarction, and in patients with impaired cardiac function. Conversely, a naturally slow heart rate, or one that is slow by virtue of sympathetic blockade induced by pharmacologic agents, may result in longer survival. This is particularly evident in the case of f-adrenergic blocking drugs, especially in patients after myocardial infarction and in those with acute as well as chronic cardiac failure, a syndrome in which there is a com- plex neurohormonal disturbance with elevated heart rate. Persistently elevated heart rate is also a feature of diabetes mellitus associated with autonomic neuropathy. Whether this also constitutes an independent risk factor for sudden and augmented mortality is not well defined. In this review, the data on the role of increased heart rate as a risk factor for mortality are examined in the context of other factors that may have therapeutic implications.