“…Collectively, these results were interpreted by these authors to indicate that excessive blood lead levels may have caused a generalized desensitization of -adrenergic receptors, which depressed the normal circulatory 92 KOPP, BARRON, AND TOW extent of the cardiac complications that develop in humans in response to chronic and acute lead poisoning (21)(22)(23)(24)(25)(26). Myocarditis (21,22), electrocardiographic abnormalities (16,23,24), altered heart rate activity (16,24), slowed ventricular systole (16,25), hypertension (16,(26)(27)(28)(29), and vascular degeneration (16,22) have all been among the reported cardiovascular aberrations detected in humans chronically and acutely exposed to toxic lead levels (Table 1). Although the threshold blood lead level that triggers cardiac involvement and symptoms of cardiotoxicity has not been determined conclusively, it is apparent that environmental and occupational lead exposures that raise blood lead levels above 100 Rg% and 60 Rg% in adults and children, respectively, are frequently associated with transient as well as permanent cardiac and vascular lesions and functional disturbances (21-29).…”