Background: Lower admission heart rate (HR) is known to predict favorable outcome in ST-elevation acute myocardial infarction. However, there are limited short-term and no long-term data available regarding the prediction value of the initial HR in patients with the full spectrum of acute coronary syndromes (ACS). In addition, it is unknown whether the HR obtained later during hospitalization for ACS (i.e., Day 2 or 3) remains prognostically valuable. Hypothesis: The aim of this study was to investigate the utility of the initial and delayed HR in predicting outcome in patients with ACS. Methods: We examined mortality at 30 days and 10 months in 10,267 patients with ACS enrolled in the oral glycoprotein IIb/IIIa inhibition with Orofiban in Patients with Unstable coronary Syndromes-Thrombolysis In Myocardial Infarction (OPUS-TIMI) 16 trial. Patients were stratified by HR and day from onset of ACS into the following groups: (1) HR <60 beats/min, (2) HR 60-80 beats/min, (3) HR 80-100 beat/min, (4) HR > 100 beats/min; and HR obtained on (1) Day 1, (2) Day 2, and (3) Day 3. Results: By univariate analysis, mortality at 30 days and at 10 months increased progressively with higher HR strata (1.4 vs. 1.6 vs. 2.3 vs. 5.6%, p < 0.001, and 2.6 vs. 4.2 vs. 6.5 vs. 11.8%, p < 0.001, respectively). Elevated HR remained associated with mortality irrespective of time from onset of ACS. Conclusions: Higher initial and delayed HR is highly predictive of higher short- and long-term mortality in patients with ACS. This is a simple marker that could be easilv used in risk assessment.