In a series of sixty-five patients with pulmonary embolism, the main clinical feature was a systolic and diastolic friction rub in three cases. Such friction rubs are found in 1 to 5% of patients with pulmonary embolism. The characteristics of the rub are identical to those of pericardial friction rubs. According to some authors, a friction rub indicates massive pulmonary embolism. However, a friction rub may be found in less severe cases if embolization involves the paracardiac lobes or segments. The rub may be caused by one or the other of the following mechanisms. Severe pulmonary embolism or a free blood clot floating in the right atrium or ventricle may produce a sound resembling a friction rub. More often, a genuine pleuro-pericardial or pericardial friction rub originates in an inflammatory reaction to a contiguous pulmonary infarct. It is important to establish accurate diagnosis of pulmonary embolism in spite of a pericardial friction rub because of the therapeutic implications. Anticoagulant therapy in sufficient dosage must not be withheld in this situation.