Background COVID-19 has been sweeping the world since it emerged in late December 2019. However, little is known about cardiac injury in hospitalised COVID-19 patients. This study is to investigate the incidence and characteristics of myocardial injury in COVID-19 patients admitted in hospital. Methods Fifty-four COVID-19 patients were enrolled in one ward in Tongji Hospital, Wuhan, China, and 5 were excluded caused by missing cardiac troponin I levels. Forty-nine participants were included in the final analysis. The clinical manifestations of hospitalised patients were analysed. Patients were divided into two groups, cardiac injury group and non-cardiac injury group, based on whether cardiac troponin I was elevated. Epidemic characteristics and laboratory test results were analysed in these two group. Results The average age of patients in the cardiac injury group was older (68.0 years old) than that in the non-cardiac injury group (61.5 years old). The percentages of patients with diabetes and critically severe pneumonia in the cardiac injury group were 38.5% and 38.5% respectively. Lymphocytes were decreased in 53.1% of all enrolled patients, but this decrease was more prominent (76.9%) in the cardiac injury group than the non-cardiac injury group (44.4%). Patients in the cardiac injury group also had lower platelet counts. Conclusions COVID-19 can cause cardiac injury in many patients. It is more common in older patients and patients with diabetes and is associated with a significant decrease in lymphocytes.