Exercise-induced left bundle branch block in a young female athlete.

An 11-year-old female, in apparent good health, was referred to our Institute because of exercise-induced left bundle branch block detected during a Master's step test performed to obtain the clearance for competitive sport. The tests that we performed to investigate the possible causes were all negative. We suspect, however, that the left bundle branch block is the initial sign of cardiomyopathy. If our suspicions are correct, close follow-up is important to chart the possible progression of the disease.