Objective To analyze the characteristics and related risk factors of myocardial injury in severe and critical coronavirus disease 2019 (COVID-19) patients and their relationship with the prognosis. Methods The clinical data of severe and critical COVID-19 patients treated in General Hospital of Central Theater Command of PLA from Jan. 2020 to Mar. 2020 were collected. The patients were divided into non-myocardial injury group and myocardial injury group. The baseline data, clinical characteristics, auxiliary examination, treatment and prognosis were compared between the two groups, and the risk factors of myocardial injury and the effect on the prognosis of the severe and critical COVID-19 patients were analyzed. Results A total of 56 patients were included, with 22 in the non-myocardial injury group and 34 in the myocardial injury group. Patients were mostly male in both groups, and there was no significant difference in gender composition between the two groups (P>0.05). Compared with the non-myocardial injury group, the age of onset was significantly higher in the myocardial injury group (78.5[70.8, 89.0] years vs 56.5[50.3, 68.3] years, P<0.01), and the proportions of patients over 65 years old and combined with coronary heart disease were significantly greater (85.3%[29/34] vs 31.8%[7/22] and 38.2%[13/34] vs 9.1%[2/22], both P<0.05). In terms of symptoms, fever (87.5%, 49/56), cough (64.3%, 36/56) and fatigue (46.4%, 26/56) were the most common ones, and there were no significant differences between the two groups (all P>0.05). For the CT findings of the lungs, the proportion of patients having patch-like/plaque-like shadows and ground-glass opacities was significantly greater in the non-myocardial injury group versus the myocardial injury group (72.7%[16/22] vs 38.2%[13/34], χ²=6.364, P<0.05), and other signs were not significantly different between the two groups (P>0.05). Compared with the non-myocardial injury group, the levels of N-terminal pro-B-type natriuretic peptide, D-dimer, procalcitonin and IL-6 were significantly higher in the myocardial injury group (4 939.5[1 817.0, 9 450.3] pg/mL vs 612.5[301.0, 1 029.5] pg/mL, 4 386.5[2 309.5, 9 635.3] ng/mL vs 850.5[343.5, 2 333.8] ng/mL, 0.46[0.23, 3.79] ng/mL vs 0.18[0.13, 0.39] ng/mL, and 138.6[41.9, 464.8] pg/mL vs 65.1[34.7, 99.3] pg/mL, respectively), and the differences were significant (all P<0.01). Multivariate logistic regression analysis showed that age ≥ 65 years old (odds ratio[OR]=18.62, 95% confidence interval[CI] 1.61-215.96, P<0.05) and D-dimer level ≥ 3 000 ng/mL (OR=15.48, 95% CI 1.45-164.77, P<0.05) were the independent risk factors for myocardial injury in severe and critical COVID-19 patients. There were no significant differences in the use of antiviral drugs, antibacterial drugs, or glucocorticoids between the two groups (all P>0.05). The mortality rate was significantly higher in the myocardial injury than that in the non-myocardial injury group (58.8%[20/34] vs 9.1%[2/22], P<0.01). Patients who received tracheal intubation, extracorporeal membrane oxygenation, continuous renal replacement therapy (CRRT) and other invasive life support measures were all in the myocardial injury group. Conclusion Older age, male gender, coronary heart disease and (or) cardiac insufficiency, and elevated D-dimer, procalcitonin and IL-6 are the risk factors of myocardial injury in severe and critical COVID-19 patients. Myocardial injury can aggravate the condition and some patients need invasive circulating breathing support, with poor prognosis and high mortality. Therefore, the above indicators need to be observed more closely and dynamically and active treatment should be given according to related factors.