Danon disease is a rare and fatal disease caused by a mutation in the lysosome-associated membrane protein 2 gene. Impaired intracellular autophagy causes lysosomal vacuoles to accumulate mainly in myocardial and skeletal muscle cells, leading to hypertrophic cardiomyopathy, skeletal myopathy, and varying degrees of intellectual disability. Two distinct childhood presentations of Danon disease are described in this report.

Risk stratification of patients with Wolff–Parkinson–White syndrome for sudden death is a complex process, particularly in understanding the utility of the repeat exercise stress test. We report a case of an 18-year-old patient who was found to have a high-risk pathway by both invasive and exercise stress testing after an initial exercise stress test showing beat-to-beat loss of pre-excitation.

It has been reported that the presence of intermittent pre-excitation indicates low risk of rapid conduction via the accessory pathway in atrial fibrillation. We report a case of a 10-year-old boy with a history of intermittent pre-excitation who presented with atrial fibrillation with very rapid conduction.