Although lung cancer frequently spreads to the heart, details of cardiac metastases of lung cancer have not been fully discussed. The authors attempted to elucidate the relationship between the mechanisms of cardiac metastasis and a variety of clinical manifestations caused by cardiac metastasis. Clinical and autopsy records were reviewed in 74 autopsied cases of lung cancer. In cases with cardiac metastasis, the metastatic pathways to the heart were determined by the macroscopic examinations, and the relationship between the metastatic pathways and the clinical manifestations were studied. Metastases to the pericardium or heart were seen in 23 cases (31%). A lymphatic metastatic pathway was detected in 18 cases (hilar lymphatic routing in 12 cases, and mediastinal lymphatic routing in 6 cases), and a hematogenous metastatic pathway was detected in 5 cases. Malignant pericardial effusion was documented in 15 of 23 cases. The metastatic pathway in 14 of 15 cases was lymphatic (hilar lymphatic routing in 10 cases, and mediastinal lymphatic routing in 4 cases). Patients showing lymphatic metastasis had higher incidence of malignant pericardial effusion than those with hematogenous metastasis (P less than 0.05). Of 23 cases of cardiac metastasis, myocardial infarction was found in 1 case, resulting from the compression of the coronary arteries by the tumor. Concurrent supraventricular arrhythmias were recorded in eight cases with cardiac metastasis. Patients with cardiac metastasis had higher incidence of arrhythmia than those without cardiac metastasis (P less than 0.05). In cases of cardiac metastasis, patients with arrhythmia were older (P less than 0.01) than those without arrhythmia. The authors concluded that the hilar lymphatic pathway is essential for early development of malignant pericardial effusion in lung cancer and that aging and cardiac metastasis may be responsible for arrhythmia in patients with lung cancer.