We report the case of a patient who developed cardiac tamponade after insertion of a central venous catheter. Often in such situations the first symptoms of this severe complication are late and thus delay correct diagnosis. In our patient the critical situation was recognized only after hemodynamic measurements and echocardiography. Emergency pericardiocentesis was followed by a dramatic improvement. The cardinal features of this serious event and the preventive measures to be taken to avoid this situation after placement of a central venous line are discussed.