Cardiovascular complications have occurred in clinical trials of interferon. We review herein experience to date of cardiotoxicity with all types of interferons in cancer patients. The most common presentations of cardiotoxicity were cardiac arrhythmia, dilated cardiomyopathy, and symptoms of ischemic heart disease, including myocardial infarction and sudden death. The cardiac effects were not related to the daily dose, cumulative total dose, or period of therapy. Some of the patients in whom interferon has caused cardiovascular sequelae have had a history of coronary heart disease or have previously been given chemotherapy with drugs known to be cardiotoxic. In most of the patients, cardiac toxicity was reversible following the cessation of the drug therapy.