CYP11B1 (Cytochrome p450, family 11, subfamily B, polypeptide 1), also called Steroid 11-beta-hydroxylase or P450C11, is a steroid hydroxylase found in the zona fasciculata. The CYP11B1 gene functions primarily in mitochondria in the zona fasciculata of the adrenal cortex to convert 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone. CYP11B1 is a member of the cytochrome P450 superfamily of enzymes. It is mapped on 8q24.3. The CYP11B1 gene contains 9 exons and spans 6.5 kb. Using RT-PCR, Kayes-Wandover and White detected CYP11B1 mRNA in human cardiac tissue samples from left and right atria, aorta, apex, intraventricular septum, and atrioventricular node, as well as whole adult and fetal heart. Ventricles did not express CYP11B1. In patients with 11-beta-hydroxylase deficiency leading to hypertension and congenital adrenal hyperplasia, Pascoe et al. identified mutations in the CYP11B1 gene.