In the past 2 decades, there have been growing evidences that resting heart rate might be a marker of risk or even a risk factor for cardiovascular morbidity and mortality. This article reviews current evidences concerning the relation between heart rate and patients' outcome in different clinical settings such as acute coronary syndromes, left ventricular systolic dysfunction, and heart failure. The relationship between resting heart rate and the development of coronary artery disease, as well as all-cause and cardiovascular mortality, has been found to be strong, graded, and independent from other risk factors. Several lines of research indicate that heart rate plays an important role in the pathophysiology of atherosclerosis and in the clinical manifestations of coronary artery disease and that it is an independent prognostic factor in all coronary syndromes. The prognostic value of elevated heart rate in patients with heart failure has been tested in several clinical trials evaluating pharmacologic heart rate-lowering agents (eg, beta-blockers). It is difficult to determine which percentage of the clinical benefit obtained with beta-blockers is related to induced bradycardia because cardiac slowing is only one of the effects of these drugs. In the BEAUTIFUL trial, a subgroup analysis conducted in patients with resting HR more than 70 beats per minute showed that treatment with ivabradine was able to improve outcome. According to the results presented in this review, we can conclude that heart rate is a predictor of death in both stable coronary artery disease and acute coronary syndromes. Elevated heart rate is also able to negatively predict clinical outcomes in patients with heart failure. However, it is still unclear if heart rate reduction per se can improve prognosis.