Risk stratification of patients with ST-segment elevation acute myocardial infarction (STEMI) is suboptimal. We assessed the prognostic value of the left ventricular ejection fraction to left ventricular end-diastolic pressure (LVEF/LVEDP) ratio in patients with STEMI who underwent primary percutaneous coronary intervention (PPCI). The study included 1,283 patients with STEMI. LVEF and LVEDP were measured at the time of PPCI. The primary outcome was 8-year cardiac mortality. Patients were divided into 3 groups: a group with a LVEF/LVEDP ratio within the first tertile (LVEF/LVEDP ratio <2; n = 437 patients), a group with a LVEF/LVEDP ratio within the second tertile (LVEF/LVEDP ratio 2 to 3; n = 422 patients), and a group with a LVEF/LVEDP ratio within third tertile (LVEF/LVEDP ratio >3; n = 424 patients). There were 109 cardiac deaths during the follow-up: 55 (17.1%), 36 (10.9%), and 18 (6.5%) deaths occurring in patients of the first, second, and third LVEF/LVEDP ratio tertiles, respectively (adjusted hazard ratio = 0.80, 95% confidence interval 0.66 to 0.97, p = 0.022 for 1 unit increment in the LVEF/LVEDP ratio). LVEF/LVEDP ratio (p = 0.035) but not LVEF (p = 0.290) or LVEDP (p = 0.145) alone improved the risk prediction of the models for cardiac mortality (p values show the difference in C-statistics between the models without and with LVEF/LVEDP ratio, LVEF or LVEDP). In conclusion, in patients with STEMI who underwent PPCI, a lower LVEF/LVEDP ratio was independently associated with increased risk of cardiac mortality up to 8 years after PPCI. The LVEF/LVEDP ratio, but not LVEF or LVEDP alone improved predictivity of multivariable models with respect to long-term cardiac mortality.