Tachycardia has been associated with worse outcomes for patients with heart failure and is also thought to have a direct adverse impact on the myocardium. This report highlights the current evidence for heart rate as both a risk factor and mediator for poor outcome for patients with heart failure. We summarize the large number of studies evaluating heart rate in patients with systolic dysfunction and newer studies that examine patients with preserved systolic function. The effect on outcomes in heart failure of medications known to slow the heart rate such as β-blockers and the more recently developed drug ivabradine are discussed. The data clearly show that a high heart rate is a marker of increased mortality. There is also a strong suggestion that a higher heart rate directly worsens outcome and that this can be mitigated by heart rate-reducing medications.