The present disclosure describes peptide inhibitors of Rho-associtated-kinase (ROCK) and their use in treating disorders including heart failure, the leading cause of combined morbidity and mortality in the United States. An inhibitory polypeptide blocks ROCK1 activity in the presence of 1 mM ATP. The binding epitope on ROCK1 was mapped using chemical cross-linking to the Activation Loop, a novel locus identifying a new class of inhibitory drugs. The peptides described will be useful against a number of important diseases such as heart disease, pulmonary hypertension, arterial hypertension, glaucoma management, insulin resistance, kidney disease, hemolytic anemia, stroke, ischemia reperfusion injury, or acute myeloid leukemia.