NDUFS4 and Arrhythmia: This finding supports the hypothesis that Ndufs4 deficiency in the cardiac conduction system itself is sufficient to cause arrhythmia in a cell‐autonomous manner, although the metabolic defect of Ndufs4−/− in neurons, cardiomyocytes, and other cell types could also contribute to arrhythmia by impacting the neurohormonal or paracrine regulation of cardiac rhythm.