Pheochromocytoma is a rare type of tumor that grows inside the middle part of an adrenal gland. Human body has two adrenal glands. They are present on the top of each kidney. Every layer of this gland produces different hormones. This middle part of the adrenal gland produces two hormones epinephrine and norepinephrine. These hormones keep heart rate and blood pressure under control. Pheochromocytoma makes the adrenal glands produce too much of these hormones.