The biological roles and their physiological mechanism of action of both nitroxyl (HNO) and hydropersulfides (RSSH) remain unknown and are a matter of intense debate in the scientific community. In the case of HNO, potential targets by which HNO can produce its effects are thiols, and thus thiol proteins, which are key components of the cardiac electromechanical machinery ruling myocardial function. It is interesting to understand the way HNO reacts because its donors have great therapeutic potential for heart failure. On the other hand, in biological systems some effects attributed to H2S may instead be due to the presence of hydropersulfides (RSSH or its deprotonated RSS- species), which might be formed on specific protein cysteine (Cys) residues. It has been proposed that protein hydropersulfide formation may serve a protective role during oxidative stress or, alternatively, may represent a hyperactivation of protein function important in certain physiological states. The aim of this project is to examine HNO reactivity functional impact with key thiol- and hydropersulfide-containing proteins. We expect that these results would allow us to clarify the mechanism of nitroxyl cardioprotection and the roles of both HNO and hydropersulfides in biological systems.