Cyclic guanosine monophosphate (cGMP) is a molecule that acts as a secondary messenger in various biological processes. It is derived from guanosine triphosphate (GTP) and plays a crucial role in signaling pathways, particularly in the regulation of blood flow and smooth muscle relaxation. In the cardiovascular system, cGMP helps to dilate blood vessels, which can lower blood pressure. It is also involved in other functions, such as neurotransmission in the nervous system and cellular responses to hormones like nitric oxide.