BackgroundThe diagnosis of myocarditis remains challenging due to its diverse clinical manifestations. We recently demonstrated the ability of magnetocardiography (MCG) to screen for myocarditis and applied it successfully to detect myocarditis in this case study of a female-to-male (FtM) patient who had undergone sexual reassignment surgery. This case highlights two significant points: first, sex differences in myocarditis may be promoted by higher levels of testosterone, and second, the ability of MCG to diagnose myocarditis. Case presentationWe report on a 38-year-old FtM patient who was hospitalized for chest pain following testosterone therapy. The patient received testosterone every 2 weeks for 6 months following his FtM surgery. Two days after the last administration of testosterone, he developed chest pain. Electrocardiography identified non-significant ST elevations in V3–6, II and aVF and echocardiography revealed reduced left ventricular ejection fraction and apical hypokinesia. High-sensitivity troponin-T (539 ng/L to 676 ng/L) and creatine kinase elevation (592 U/L) were elevated. Coronary CT angiography ruled out coronary artery disease. Cardiac magnetic resonance imaging confirmed suspected myocarditis.Additionally, we used MCG to detect abnormalities in the electromagnetic field. A pathologic vector (0.179) supported the diagnosis of myocarditis in this patient. During therapy with ibuprofen the vector improved to 0.067 after 3 weeks accompanied by symptom improvement. ConclusionTestosterone treatment may have promoted myocarditis in a FtM individual. Additional MCG assessment was consistent with a diagnosis of myocarditis and highlights the promising potential of this method to facilitate diagnostic screening for cardiomyopathy in the future.