Carbon monoxide: A vital signalling molecule and potent toxin in the myocardium

► The protective and deleterious effects of carbon monoxide (CO) in the myocardium are considered. ► Endogenous CO is clearly protective against ischemia/reperfusion injury. ► Protective effects of CO likely involve multiple second messenger pathways and ion channels. ► At higher concentrations, CO is cardiotoxic and pro-arrhythmic. ► The pro-arrhythmic effects of CO are likely to involve regulation of alternative ion channels.