Senning’s operation is a palliative operation of non-corrected transposition of the large vessels, which without surgical treatment is incompatible with long-term survival. A disadvantage of this solution is that the right ventricle is in the position of the systemic ventricle, and numerous supraventricular disorders of the rhythm, in particular sinoatrial node dysfunction. The authors examined, using the loading test, 12 boys and 5 girls with transposition of the large vessels after Senning’s operation. The patients were 7 - 16 years old, mean 11.8 years and did not have any subjective complaints. The authors used the method of bicycle ergometry with James’ loading protocol. They examined the tolerance of the subjects to loads and none of the patients reached during the maximal load the normal level of maximal cardiac rate. Dysfunction of the sinoatrial node was recorded at the onset of the test in 10 patients. Only in one patient the sinus rhythm was not restored during the maximal load. In this patient also subsequent examinations confirmed a serious impairment of the sinoatrial node and he has an implanted pacemaker. Loading tests are suitable for evaluating the severity of disorders of the rhythm and testing of physical fitness in patients after Senning’s operation.

        Key words: loading tests, bicycle ergometry, transposition of the large vessels, Senning’s operation