BACKGROUND: While numerous studies have investigated the onset features of myasthenia gravis (MG) complicated with myocarditis, there are few articles focusing on the prognosis of patients with both diseases. This study aims to examine mortality in patients with MG who also have myocarditis, and to summarize the clinical characteristics of deceased patients with both conditions. RESULTS: A total of 91 patients with MG were included in our study, of which 19 (20.9 %) were diagnosed with myocarditis. Shorter MG duration, thymoma, history of myasthenia crisis (MC) and use of immune checkpoint inhibitors (ICIs) were risk factors for developing myocarditis in MG patients. Among the 13 myocarditis-MG patients who did not receive ICIs, 11(84.6 %) had thymoma and 5 (71.4 %) of the 7 tested were positive for titin-IgG. In all myocarditis-MG patients, 11 (57.9 %) died from myocarditis (average age 51 ± 18 years), with 9 (81.8 %) having thymoma and 5 (45 %) having a history of myasthenia crisis. Compared to the mortality rates of MC patients (16.1 %) and the general MG patients (1.8 %), the mortality rate of myocarditis-MG patients is significantly higher. CONCLUSIONS: The study highlights that MG patients with myocarditis face a significantly increased risk of mortality. Thymoma and a history of MC were identified as potential risk factors for mortality, irrespective of prior ICI use.