OBJECTIVE: To assess the clinical utility of the Shock Index (ratio of the heart rate to systolic blood pressure) to distinguish ruptured (rEP) from unruptured ectopic pregnancy (urEP). DESIGN: A prospective cohort study including all patients presenting to the emergency room in 2008 with a diagnosed EP with a plan for surgical treatment were enrolled at the University of Miami. MATERIALS AND METHODS: A prospective cohort study including all patients presenting to the emergency room in 2008 with a diagnosed EP with a plan for surgical treatment were enrolled at the University of Miami. The SI was calculated upon initial patient presentation. Outcome was classified as rEP or urEP based on the intraoperative findings and tubal rupture verified by the pathology report. Standard statistical comparisons were performed between the two groups (rEP vs. urEP). RESULTS: Sixty-four surgically treated women were enrolled and classified as rEP (42) or urEP (23). The SI was significantly higher in the group of women with rEP compared to the group with an urEP (mean ± SD, 0.74 ± SD vs. 0.67 ± SD, P=0.042). The estimated blood loss was significantly higher in the rEP group compared to the urEP (mean ± SD, 363 ± 2703 vs.63.1 ± 43, P=0.01). There was a significant positive correlation between the SI and hemoperitoneum in those subjects with more than 100 cc of EBL (r=0.573, P<0.01). Women with a SI of 0.81 or greater are significantly more likely to have a rEP [RR: 1.67 (95% CI 1.27-2.21, P= 0.01)]. Utilizing 0.81 SI value or greater as a cut off to predict a rEP carries a high positive predictive value 94% (sensitivity 35%, specificity 95%, negative predictive value 44%). CONCLUSION: Patients who have a SI of 0.81 or greater are 1.67 times more likely to be ruptured. A simple calculation based on heart rate and blood pressure (SI) can be used to predict presence of rupture of an ectopic pregnancy and assist in triage of operative candidates.