Cyanide poisoning is a form of histotocix hypoxia, because the cells of an organism are unable to use oxygen, primarily through the inhibition of the enzyme cytochrome c oxidase. This enzyme is part of the organelle mitochondrion.
Mitochondria are described as "the powerhouse of the cell" because they generate most of the cell's supply of adenosine triphosphate (ATP), used as a source of chemical energy. In fact the cytochrome proteins in the membrane of the mitochondria are involved in oxidative phosphorylation, the process by which ATP is made.
Mitochondria, then, are instrumental in the process of cellular respiration in organisms. The product ATP of cellular respiration is sometimes called the "universal chemical energy currency of life".
The cyanide ion binds to the cytochrome proteins, where oxygen molecules would have (in normal respiration), so the cells are starved of oxygen which is a vital ingredient for the production of energy in cells and hence metabolism.
Chemical compounds that produce cyanide ions when dissolved in water include for example hydrogen cyanide gas and the crystalline solids potassium cyanide and sodium cyanide. Chemicals such as these then are poisonous to living organisms.