Cardiac myxomas from eight patients were examined cytogenetically in short-term cultures. Cultures could not be established in two of the eight cases. Chromosomally abnormal clones occurred in two of the myxomas; their karyotypes were 45,X,-Y,+7,-18 and 45,X,-Y. In three other myxomas, we found a rare kind of telomere-to-telomere translocation between chromosomes. The telomeres predominantly involved in these three tumors were the 2qter (the end of the long arm of chromosome 2), the 12pter (the end of the short arm of chromosome 12), and Yqter (the end of the long arm of the Y chromosome), respectively. In one other myxoma, 20% of the cells were tetraploid. These findings support the concept that myxomas are neoplastic; those with an abnormal clone may even have malignant potential. The unusual telomere-to-telomere translocations were not observed in a clonal pattern. They may represent a specific type of chromosomal instability associated with a defect in repair or replication of telomeric DNA.