The motor protein myosin initiates movement in all cells of the body by tracking on actin filaments. Myosin activity is enhanced by the calcium-dependent myosin light chain kinase which phosphorylates a regulatory light chain subunit of myosin while myosin light chain phosphatase dephosphorylates the light chain. Impaired light chain phosphorylation causes heart failure, and failed smooth muscle functions involving the hollow organs of the body (blood vessels, airways, intestines, and bladder). The phosphorylation of myosin is not controlled by a simple cascade but different integrative signaling modules forming cellular networks with different second messenger systems. Our work uses many biochemical, biophysical, cell biological and physiological tools to provide novel perspectives on derangement of myosin phosphorylation in human diseases, including heart failure, asthma, and aortic aneurysms and dissection.