A 69-year-old male presented with symptoms of fulminant lung embolism and, despite immediate therapy with plasminogen activator, died of acute right heart failure. At autopsy multiple tumor cell emboli were detected in small pulmonary vessels in addition to widespread liver metastases from an urothelial carcinoma. - In a 23-year-old female a malignant gastric ulcer and multiple liver metastases were diagnosed at initial presentation. She too died from pulmonary hypertension due to a series of lung embolisms which occurred despite heparin therapy. At autopsy, many small pulmonary arteries were filled with adenocarcinoma cells; the primary gastric tumor and liver metastases were confirmed. These cases demonstrate that the shedding of tumor cells from hepatic metastases can obstruct the pulmonary vessels and lead to acute cor pulmonale. Tumor cell emboli should be considered in the differential diagnosis of acute pulmonary hypertension, especially in patients with a known tumor. They may, however, also represent the first clinical signs of previously unrecognized malignancy.