Potentially serious cardiovascular changes occur in alcoholics as a result of carbimide‐ethanol reactions (CERs). Hypotension and tachycardia often occur when blood acetaldehyde levels increase. Hypotension with bradycardia can also occur secondary to vagal stimulation, the result of retching or vomiting. Conservative procedures (e.g., modified Trendelenburg's position) are usually effective in reversing the hypotension but in severe reactions active treatment (intravenous fluids, O2, and drugs) may be indicated. Three case reports are presented to illustrate cardiovascular responses during CERs; for comparison, changes for one subject during a disulfiram reaction are also presented. Caution is recommended in screening alcoholics before treatment with carbimide or disulfiram so as to rule out cardiovascular, hepatic, or renal diseases.Clinical Pharmacology and Therapeutics(1981)29,40–46; doi:10.1038/clpt.19