Phosphodiesterase (PDE) is an enzyme that plays a crucial role in cellular signaling by breaking down cyclic nucleotides, such as cyclic AMP (cAMP) and cyclic GMP (cGMP). These cyclic nucleotides are important for various physiological processes, including regulating blood flow, muscle contraction, and neurotransmission. By hydrolyzing these molecules, phosphodiesterases help control the duration and intensity of their signaling effects. There are several types of phosphodiesterases, each with specific functions and tissue distributions. For example, PDE5 is primarily found in the smooth muscle of blood vessels and is targeted by medications for treating erectile dysfunction. Understanding phosphodiesterases is essential for developing therapies for various conditions, including cardiovascular diseases and mental health disorders.