Tehran University of Medical Sciences The Research in Heart Yield and Translational Medicine (RHYTHM) 3115-7270 21 1 2026 04 26 98 102 Ehsan Shahverdi Baqiyatallah University of Medical Sciences, Tehran, IR Iran Gayathri Santhosh Kumar Department of Cardiology, Rhythmology and Intensive Care Medicine, Med. Klinik I, Klinikum Osnabrück, Osnabrück, Germany. Carsten Schneider Department of Cardiology, Rhythmology and Intensive Care Medicine, Med. Klinik I, Klinikum Osnabrück, Osnabrück, Germany. Mathias Lange Department of Cardiology, Rhythmology and Intensive Care Medicine, Med. Klinik I, Klinikum Osnabrück, Osnabrück, Germany. 2025 08 01 2025 08 09 Background: Primary malignant pericardial mesothelioma (PMPM) is an exceptionally rare and aggressive cancer originating from the mesothelial lining of the heart. This distinct and challenging oncologic entity is typically discovered at an advanced stage due to vague, nonspecific symptoms—most commonly chest pain and dyspnea. These clinical features often mimic more common conditions, making early detection difficult. Diagnostic confirmation usually requires detailed histopathologic analysis, often obtained through surgical procedures or postmortem examination. The disease’s elusive nature and rapid progression contribute to its generally poor prognosis, underscoring the need for heightened clinical awareness and advanced diagnostic strategies. Case Report: A 58-year-old patient was diagnosed with malignant pericardial mesothelioma, which progressed rapidly and resulted in death within 1 month of diagnosis. Conclusions: PMPM remains a rare and highly aggressive cancer characterized by swift, fatal progression. Diagnosis is difficult because of nonspecific clinical symptoms. Accurate diagnosis is essential for subsequent treatment planning. Nonetheless, limited treatment alternatives, coupled with the minimal effectiveness of immunotherapy in advanced disease, highlight the pressing need for further research and therapeutic advances. https://jthc.tums.ac.ir/index.php/jthc/article/view/2322 https://jthc.tums.ac.ir/index.php/jthc/article/download/2322/1251