Exposure to heavy metals is an important source of DNA damage in human beings and in animals. Heavy metals like iron, copper, chromium, lead, zinc, mercury, nickel etc. and reactive oxygen species enhance peroxidation of lipids and DNA damage. Elements like arsenic, nickel and cadmium are the ambassadors of mutagenic changes in cell. In mammalian cells it was found that DNA single strand breaks chromosomal aberrations occurred and sister chromatids exchange due to various nickel salts. Cadmium causes cancer in tissues of animals. Exposure to cadmium develops cancer in prostate gland, kidney, liver and stomach. However, some heavy metals directly damage the DNA thus generating negative results. The synthesis of nucleic acids and proteins is affected by cadmium. However, cadmium does not have a strong mutagenic nature when compared to other heavy metals.