Purpose: Acute type A aortic dissection (ATAAD) is a dissection involving the ascending aorta within 14 days of symptom onset. Acute myocardial ischemia is associated with short-term mortality in patients with ATAAD. However, its relevance to ATAAD’s surgical timing and prognostic implications is unknown. Methods: This retrospective study enrolled 277 patients at our tertiary center between March 1997 and January 2019 and investigated their admission electrocardiograms. Twenty-one patients with left ventricular hypertrophy or left bundle branch block were excluded, and the records of 256 patients eventually underwent data collection, review, and multivariate analysis. Results: In patients with acute myocardial ischemia, the incidence of aortic root involvement, acute coronary involvement, and preoperative stroke was significantly higher. Acute myocardial ischemia was unassociated with 30-day or in-hospital mortality in patients who underwent surgery within 7 h of symptom onset. However, it was independently associated with the 30-day mortality and postoperative stroke when the 7-hour window had elapsed. Conclusions: As a time-dependent surgical prognosticator in ATAAD, acute myocardial ischemia was unassociated with short-term mortality in patients surgically operated within 7 h of symptom onset. Conversely, it was an independent factor for the 30-day mortality and postoperative stroke when the 7-hour window had elapsed.