Background: Myocarditis, an inflammatory condition, may result from multifactorial causes but in association with lymphoma is an extremely rare presentation. We report a nodal anaplastic lymphoma kinase (ALK) positive anaplastic large-cell lymphoma (ALCL) case in a young adult who was detected with systemic dissemination and showed findings of myocarditis on postmortem examination. Case presentation: An 18-year-old female presented with chief complaints of fever, fatiguability, and backache accompanied by loss of weight and appetite for 2 months. All the systems, on examination, appeared normal. Whole-body positron emission tomography–contrast enhanced computed tomography (PET–CECT) scan revealed ¹⁸F-fluorodeoxyglucose (FGD) avid multiple lymph nodes involving cervical, diaphragmatic, thoracoabdominal, and inguinal regions along with uptake in the wall of the sigmoid colon. The excisional node biopsy revealed a diagnosis of ALK-positive ALCL. During this time, the patient developed paroxysmal supraventricular tachycardia (PSVT) and recurrent hypoglycemic episodes and succumbed to her illness subsequently. Septicemia-related cardiogenic/refractory shock was kept clinically as the cause of the death. A detailed postmortem histopathological examination revealed advanced stage presentation of ALCL with systemic involvement of the large intestine, pancreas, ovaries, skin, skeletal muscle, urinary bladder, and soft tissue [stage IV Burkitt's Edema (BE)]. In addition, findings of lymphoma-associated myocarditis, extramedullary hematopoiesis, and secondary hemophagocytosis were evident. Conclusion: This case represents a very rare case of ALK-positive ALCL that developed myocarditis as diagnosed on postmortem examination. Myocarditis should be suspected in a case of lymphoma with arrhythmia/PSVT so that early intervention can be planned.