Contamination by heavy metals has attracted increasing attention considering the ability of these elements in producing serious consequence to ecosystem, and especially on animals health. Due to their widespread use in human activities such as industry, agriculture and even as medicine (e.g. arsenic, selenium and platinum), numerous health risks may be associated with exposure to these substances. All heavy metals, in spite some of them are essential micronutrients, have their toxic effects because of their bioaccumulation on living organisms, and so generally exhibit chronic toxicity via metabolic interference and mutagenesis. They are also classified as carcinogens (known or probable) according to the U.S. Environmental Protection Agency, and the International Agency for Research on Cancer (IARC). In the present paper, the lead, cadmium and chromium disease processes (induced toxicity) were summarized with particular emphasis on the generation and the role of reactive oxygen species (ROS), the unifying factor in determining toxicity for all these metals. پرونده مقاله