Background— The role of the vasopressin system after acute myocardial infarction is unclear. Copeptin, the C-terminal part of the vasopressin prohormone, is secreted stoichiometrically with vasopressin. We compared the prognostic value of copeptin and an established marker, N-terminal pro-B-type natriuretic peptide (NTproBNP), after acute myocardial infarction. Methods and Results— In this prospective single-hospital study, we recruited 980 consecutive post–acute myocardial infarction...