Metastasis to the heart is compared with that to other target sites in terms of incidence, tissue susceptibility, and cancer cell injury within the microcirculation. At necropsy the myocardium is the sixth most common site for arterial metastasis among eight target organs in ten different types of disseminated primary cancer. However, the metastatic efficiency index (incidence/blood flow) indicates that the myocardium is no less susceptible to metastatis per unit of cancer cells delivered than most other sites examined. The analyses also indicate that cancer cells causing myocardial metastasis are mainly derived from metastatic or primary tumours in the lungs. Experiments on laboratory animals suggest that the failure to develop myocardial metastasis in 80 to 98% of patients with metastatic cancer is at least partially due to lethal, deformation-associated, mechanical damage inflicted on cancer cells trapped within the myocardial microvasculature.