The aim of this article is to review an actual data concerning biological effects of carbon monoxide (CO). This gas, already known as a dangerous poison is also described as an important regulatory substance, like to nitric oxide. There are mentioned experiments concerning exogenous induction of hem oksygenase-1 (HO-1) enzyme, which is responsible for endogenous CO generation by hem catabolism. The another way to increase CO levels is to administer it as a Carbon Oxide Releasing Molecules (CORMs). Thus, it is proven that CO in small doses exerts various beneficial effects on cardiovascular system functions, through vasodilatation, cardioprotection, as well as beneficial effect on endothelium. Additionally, CO exerts anti-imflammatory and anti-oxidating effects. CO/HO-1 system is also involved in attenuation of some metabolic and neurodegenerative processes. In respect to toxicological properties of CO, all shown data clearly suggest, that in adequate dose CO may be a valuable drug to use in cardiovascular disorders.