Cardiac myxoma: A benign tumor of the heart and the most common type of heart tumor in adults. Cardiac myxomas can appear in an isolated case or in families, sometimes as part of an hereditary syndrome called the Carney complex. Some families have the Carney complex variant as well as the trismus-pseudocamptodactyly syndrome (Hecht syndrome). A mutation in the perinatal myosin heavy chain causes this Carney complex variant, suggesting that mutated contractile proteins play a role in the development of cardiac myxomas.