Objectives: We hypothesized that prehopsital ECG scores can identify ST-segment elevation myocardial infarction (STEMI) patients in whom time delay is particularly important for myocardial salvage. Methods: We evaluated the Anderson-Wilkins (AW) score (which designates the acuteness of ischemia) and grade 3 ischemia (GI3) (which identifies severe ischemia) in the prehospital ECG and compared them to the myocardial salvage index (MSI) assessed by cardiac magnetic resonance. Results: In 150 patients, system delay (alarm to balloon inflation) (β = -0.304, p < 0.001) and AW score (β = 0.364, p < 0.001) correlated with MSI. AW scores ≥3 (p < 0.001) and GI3 (p = 0.002) predicted the MSI. We formed 4 subgroups combining AW scores (<3 or ≥3) and grades of ischemia (<GI3 or =GI3), yielding a prehospital salvage score of 1-4, which predicted the MSI (p < 0.001), left ventricular ejection fraction at 3 months (p = 0.017), infarct size (p < 0.001), and troponin T (p < 0.001). MSI was only dependent on system delay in patients with acute ischemia (AW score = 3) with (β = -0.687, p = 0.005) or without (β = -0.454, p < 0.001) severe ischemia (GI3). Conclusion: In patients with STEMI, the novel prehospital salvage score identifies subgroups in which myocardial salvage is particularly time dependent.