No data exist in the English-language literature about patients with Barlow disease associated to Steinert syndrome and little is known about the employment of hypothermic cardiopulmonary bypass (CPB) and hyperkalemic cardioplegia in these patients. We present our experience with six patients affected by myxomatous degeneration associated to Steinert disease undergoing complex mitral valve repair. In all patients we employed mild hypothermic CPB (31 degrees C) and myocardial protection was achieved, in the entire cohort, by the use of blood hyperkalemic cold cardioplegia. The postoperative course was uneventful in all patients and neither shivering nor generalized muscle contraction were observed. Furthermore, all patients have remained well on an outpatient basis. Hypothermic CPB and hyperkalemic cardioplegia can be safely employed in patients with Steinert syndrome requiring complex cardiac surgery. Further large studies are necessary to confirm our findings.