NDUFAB1 and cardiomyopathy: Measuring mitochondrial membrane potential (ΔΨm) in isolated cardiomyocytes with the potential-sensitive fluorescent probe tetramethyl rhodamine methyl ester (TMRM) showed that NDUFAB1 ablation significantly decreased ΔΨm even at 6 weeks (Fig. 2b) when the heart morphology and function were normal (Fig. 1), indicating mitochondrial dysfunction is an early event in cKO mice preceding the onset of cardiomyopathy.