A 31-year-old white male patient was transferred from a local district hospital for suspected pericardial mass. Two months earlier he had been admitted there for worsening shortness of breath and subsequently was diagnosed with a large pericardial effusion. He had no other pertinent past medical history. After pericardiocentesis (1.5 L) there was no evidence of malignant cells on cytology, and a computed tomography scan did not reveal any abnormality. Thus, the incident was interpreted as (viral) infectious pericarditis and the patient clinically improved under anti-inflammatory medication within 4 weeks. After that, while on a holiday in Tunisia, he again reported worsening shortness of breath. On day 6 of his holiday, he suddenly passed out and was admitted to a local hospital for unexplained syncope, where again a large pericardial effusion was seen. This time, after another pericardiocentesis (1 L), a pericardial mass was suspected by echocardiography and the patient was transferred back to Germany for further workup.Cardiovascular magnetic resonance on the day of admission to our center revealed a large inhomogeneous mass within the pericardium and the mediastinal space infiltrating the big vessels, as well as the right atrium (Figure 1 and online-only Data Supplement Movies I and II). The mass severely compressed the entire heart, leading to hemodynamic compromise. Therefore, in our multidisciplinary oncology conference, the decision for urgent surgical sampling for