Fragmentation of the mitochondria and impairment of mitochondrial respiration resulting from conditional cardiac-specific combined ablation of MFN1 and MFN2 in the adult murine heart have been reported to result in a severe lethal dilated cardiomyopathy after 6–8 weeks, implicating a role for the Mitofusins in maintaining normal mitochondrial function in the adult heart (Chen et al., 2011). The gene discussed is MFN2; the disease is dilated cardiomyopathy.