5-fluorouracil is a drug that is widely used in cancerology. Its cardiotoxicity must be known, as it is not exceptional and potentially dangerous. Two cases are reported in which the coronary insufficiency was documented and recurred when 5-fluorouracil was reintroduced. The mechanism of cardiac toxicity seems to be coronary spasm, as shown by exercise tests and the normal results of coronary arteriography. It seems preferable to refrain from using 5-fluorouracil after a recent myocardial infarction or in patients with unstable angina. Reintroduction of the drug is usually followed by recurrence of cardiotoxicity, even under coronary vasodilators.