Nkx2-5183P/+ neonatal cardiomyocytes mitochondrial activity measured as basal respiration, ATP production, proton leak, maximal respiration, spare respiratory capacity, and nonmitochondrial respiration. (n = 5) *P < 0.05; **P < 0.01; ***P < 0.001, unpaired t test equal variance 2 tailed. OCR, oxygen consumption rate.