Mitochondria, as almost any high school biology student will tell you, are the “power plants” of cells and the heart performs the same role for the body. Mitochondria are present in 500 to thousands of copies per cell and are inherited strictly from the mother. What happens, one might wonder, when something goes awry in the mitochondria of the heart? Will this weaken the heart? Not surprisingly, the answer is yes, but a bigger question is what role the process of selection in the mother’s oocytes plays in transmitting defective mitochondria to her offspring. Writing in the February 15 issue of Science, Douglas Wallace and colleagues at UC Irvine report that they introduced severe mitochondrial mutations affecting oxidative phosphorylation into a female mouse line. The most severe mutations were eliminated after only four generations of oogenesis, indicating that some mitochondrial selection does occur in the formation of oocytes. Not all mitochondrial mutations, however, ended up in the trash can. One set of milder mutations was retained across many generations even though progeny carrying them developed cardiomyopathies. Some mitochondrial mutations can therefore be propagated through females in the population despite their deleterious effects. Expanding these findings to humans is an important next goal.