Since functional mitochondria in the heart are required not only to provide energy for the pumping function but also to cope with externally or internally induced changes—e.g., during and after myocardial infarction—we hypothesized that a non-cell cycle–related function of p27, according to our data most likely in the mitochondria, could also be important for the heart. The gene discussed is CDKN1B; the disease is myocardial infarction.