Four fatal cases of diltiazem overdose are described and compared with previously published cases. Clinical sequelae include all grades of heart block, hypotension and ultimately death. Management includes gastric lavage and oral administration of activated charcoal at presentation. Further symptomatic treatment with inotropic agents and temporary cardiac pacing may be required. If these measures are successful, recovery occurs within 36 hours in uncomplicated cases. Toxicological data have been reviewed but currently drug levels can only offer a retrospective analysis of the severity of overdoses. As the use and risk of abuse of diltiazem increases, these reports serve to highlight the possible hazards and to alert physicians to what must be regarded as a dangerous and potentially lethal drug in overdosage.