The etiology of pericardial effusion can be unusual and surprising. “Behind the curtain” of cardiac tamponade unusual causes may be hidden. Whereas pericardial effusion caused by metastatic disease is quite common [1, 2] with about 40% of all cases of pericardial tamponade in our registry, primary cardiac tumors are rare. They amount to only 3% of all cardiac tumors. Cardiac tumors originating from the vascular bed are even rarer [3]. We present the case of a 52-year-old male (178 cm, 79 kg), who was admitted initially to a regional county hospital with fatigue and fever. His medical biography was uneventful except for arterial hypertension and a thyroid cyst. His ECG showed an elevated heart rate of 112/min and low voltage; blood pressure was 105/70 mmHg. Echocardiography demonstrated a pericardial effusion with tamponade. He underwent pericardiocentesis. Cytological analysis of the effusion contributed to the diagnosis of “idiopathic” hemorrhagic effusion of the pericardial sac. An infectious etiology was assumed. Treatment with corticoids was initiated. The effusion recurred nevertheless. Pericardiocentesis was again carried out, now in a nearby university hospital. Computed tomography ruled out aortic dissection, but gave no clue to the etiology of the hemorrhagic pericardial effusion. After an extensive investigation by cytology of the pericardial fluid and the peripheral blood, the diagnosis of recurrent idiopathic hemorrhagic pericardial effusion was maintained. 3 months later, tamponade was diagnosed again in the regional hospital (Figure 1) and the patient was sent to our referral center for further investigation and treatment. In the first seconds of contrast injection, coronary angiography revealed a normal coronary tree (Figure 2a), but, in later images, showed multiple depots of contrast media originating from the coronary vasculature (Figure 2b) highly suggestive of an angiosarcoma or another form of neovascularization of the coronaries. Shunts into the pericardial sac and the lower vena cava were demonstrated as was an ectatic left and right arteria cerebri media, suggestive of an aberrant malformation. Due to tamponade, pericardiocentesis was performed and 1,420 ml of hemorrhagic effusion (hemoglobin 7,5 mg%) were removed from the pericardial sac. Cytology for malignant cells, microbiology, immunoserology and the polymerase chain reaction for RNA and DNA of cardiotropic microbial agents (entero-, adeno-, parvovirus B19, human herpesvirus 6 and influenza viruses, Epstein-Barr virus, Chlamydia pneumoniae, Borrelia burgdorferi, HIV, hepatitis C virus) in both the pericardial fluid and the blood were negative. The pigtail catheter was left in place, but tamponade recurred within 48 h. Therefore, the patient was transferred to cardiac surgery with the primary intention to stop the continuous leakage of blood from the sarcomatous lesions into the pericardium. On this occasion, a definite histology could be established, which confirmed the suspected diagnosis of hemangioendotheliosarcoma. Despite this desperate effort, the bleeding into the pericardial sac could not be stopped from the multiple angiomatous lesions and the patient died consequently. This case and these images demonstrate that behind the curtain of pericardial tamponade rare primary cardiac tumors can be hidden [4]. Although CT and MRI can contribute to the diagnosis [5], but did 1 Department of Internal Medicine and Cardiology, University Hospital of Internal Medicine Giesen and Marburg GmbH, Marburg, Germany, 2 Department of Internal Medicine and Cardiology, Hospital Crailsheim, Germany, 3 Institute of Pathology, University Hospital of Internal Medicine Giesen and Marburg GmbH, Marburg, Germany, 4 Department of Cardiac Surgery, University Hospital of Internal Medicine Giesen and Marburg GmbH, Marburg, Germany.