For example, we examined the nuclear:mitochondrial DNA ratio in Python hearts as mtDNA is lost when DNM1L is down-regulated and mitochondrial fission impaired [28], However, there was no alteration in the nuclear:mitochondrial DNA ratio in Python hearts at any stage before the development of overt CHF and even at this stage only some Python hearts showed an increased ratio (Figure 6B). This evidence concerns the gene DNM1L and congestive heart failure.