Mediastinal neoplasms are rare in the elderly, and clinical suspicion is the first and most important step of differential diagnosis. Mediastinal tumors can be misdiagnosed because their symptoms or signs can overlap with cardiovascular diseases, which have a higher prevalence among the older population. The diagnostic process should be managed with multimodality imaging and clinical judgement. Here, the case of a 74-year-old male patient, who presented with shortness of breath, is examined. A chest X-ray revealed an increased cardiothoracic ratio, and he was diagnosed with hemopericardium following an emergent chest computed tomography. In the echocardiography, it was suspected that a hyperechogenic area adjacent to the heart might be due to a mass, and further examinations confirmed a mediastinal neoplasm. A surgical biopsy was performed, and it was determined to be a mesenchymal tumor. To conclude, clinicians should keep in mind the possibility of paracardiac neoplasm in the elderly, as well as in other age groups, when encountering mediastinal widening so that the patient can be protected from unnecessary interventions such as pericardiocentesis.