The clinicopathologic features of 107 cardiac myxomas are presented. Eighty-one were in the left atrium, 18 in the right atrium, and 8 were biatrial or located in the ventricles. The mean age at presentation was 50 years and did not vary significantly by sex, race, or site in the left or right atrium. Histologically, 41% of tumors had surface thrombus; 41%, fibrosis; 23%, mitotic activity; 20%, calcification; 17%, gamma bodies; 8%, ossification; 7%, extramedullary hematopoiesis; 3%, mucin-forming glands; 3%, atypical cells simulating malignancy; and 1% had thymic rests. A majority of myxomas was immunohistochemically positive for QBEnd throughout the lesion, but in most tumors, factor-VIII related antigen was limited to the surface cells. A minority of myxomas stained for antismooth muscle actin and Ulex europaeus; KP-1 and cytokeratin were always negative. Right atrial tumors were more likely calcified than those in the left atrium. Embolic tumors were less often fibrotic than nonembolic myxomas and were more likely thrombosed and extensively myxoid with an irregular frond-like surface. Fibrotic and non-thrombosed tumors had a longer mean duration of clinical symptoms and were found in older persons. Recurrent, multiple, and familial myxomas were more often found in younger women and, more likely irregular surfaced and histologically myxoid; however, they were not likely to be histologically atypical, cellular, or incompletely excised. Five tumors caused the death of the patient by emboli to the brain or heart, but none metastasized. The histology of myxomas varied by site, clinical presentation, patient age, and immunohistochemical findings.