Background There is paucity of data regarding the prognostic implications of first-degree atrioventricular block in patients with acute anterior myocardial infarction as a distinct group. The aim of this study was to elucidate the association of prolonged PR interval with hospital clinical outcomes in patients with treated with thrombolysis. Methods Three hundred consecutive patients with a first acute anterior ST-segment elevation myocardial infarction undergoing thrombolysis between October 2017 and March 2018, were retrospectively enrolled in this study. They were divided into two groups based on PR interval on admission: PR interval ≤200 ms, and PR interval > 200 ms. Hospital mortality and complications were compared between the 2 groups. Results Of the 300 patients, 26 (8.66%) had first-degree atrioventricular block on initial presentation. Overall, hospital death occurred in 20 (6.66%) patients. Patients with PR interval > 200 ms had a higher hospital mortality rate (26.9%) than those without (4.7%, p < 0.001). In multivariate Cox regression analysis, only left ventricular systolic function and PR interval were independent predictors of hospital mortality (odds ratio = 1.031; 95% confidence interval: 1.008–1.056, p = 0.009 for PR interval). Conclusion In patients with a first acute anterior ST-segment elevation myocardial infarction treated with thrombolysis, first-degree atrioventricular block was associated with increased hospital mortality and a worse prognosis.