Objective:To analyze the clinical value of dynamic electrocardiogram combined with serum brain natriuretic peptide (BNP) and creatine kinase isoenzyme (CK-MB) levels in evaluating the severity of respiratory tract infection complicated with viral myocarditis.Methods:A total of 125 patients with respiratory tract infection who were admitted to the Affiliated Run Run Shaw Hospital of Medical School, Zhejiang University from January 2018 to December 2022 were selected retrospectively. They were divided into the complication group (71 cases) and the non-complication group (54 cases) according to whether they were complicated with viral myocarditis. Dynamic and conventional electrocardiogram characteristics were compared. Serum BNP and CK-MB levels in the complication group and the non-complication group at admission were analyzed. Dynamic electrocardiograms and serum BNP and CK-MB levels of patients with different severity of myocarditis were comparatively analyzed. The value of combined diagnosis was analyzed.Results:The detection rates of atrial premature beats and sinus tachycardia by dynamic electrocardiogram were higher than those by conventional electrocardiogram: 38.03% (27/71) vs. 22.54% (16/71), 28.17% (20/71) vs. 14.08% (10/71) ( P<0.05). Serum BNP and CK-MB levels in the complication group were higher than those in the non-complication group: (104.26 ± 10.75) ng/L vs. (54.11 ± 5.69) ng/L, (17.89 ± 1.86) U/L vs. (13.46 ± 1.42) U/L ( P<0.05). The detection rates of atrial premature beats, sinus tachycardia, burst ventricular tachycardia, first-degree atrioventricular block, ST segment change and low QRS voltage, serum BNP and CK-MB levels in patients with respiratory tract infection complicated with severe viral myocarditis (37 cases) were higher than those in patients with mild viral myocarditis (34 cases): 51.35% (19/37) vs. 23.53% (8/34), 43.24% (16/37) vs. 11.76% (4/34), 32.43% (12/37) vs. 11.76% (4/34), 29.73% (11/37) vs. 8.82% (3/34), 43.24% (16/37) vs. 14.71% (5/34), 24.32% (9/37) vs. 5.88% (2/34), (107.19 ± 10.56) ng/L vs. (101.08 ± 10.18) ng/L, (18.33 ± 1.85) U/L vs. (17.41 ± 1.76) U/L ( P<0.05). Compared with clinical pathological diagnosis, Kappa values of dynamic electrocardiogram, BNP at admission, CK-MB at admission and combination of the three for diagnosing acute upper respiratory tract infection complicated with viral myocarditis were 0.784, 0.765, 0.733 and 0.879. The sensitivity and accuracy of combined diagnosis were higher. Conclusions:Dynamic electrocardiogram combined with serum BNP and CK-MB can better help to evaluate the severity of respiratory tract infection complicated with myocarditis. Therefore, they are worthy of monitoring.