Two hundred thirty-one euthyroid, seriously ill cardiac patients have been treated with radioactive iodine (I131) since February, 1950, in the department of radiation therapy and the cardiac outpatient department of the Cedars of Lebanon Hospital in Los Angeles. Of particular interest is the analysis of the original 100 patients treated four years ago. Radioiodine treatment for euthyroid cardiac invalids was pioneered by Blumgart and his associates in March, 1947. They reported, in August, 1952, their results in the treatment of 39 patients followed for 40 months.1In April, 1951, Wolferth and his group2gave account of 28 patients treated with radioiodine for intractable angina pectoris. Stuppy,3Jaffe,4Pobirs,5and Rosenfeld6reported upon 95 treated patients in November, 1951, and upon end-results in 100 patients in June, 1952.7In 1952, Chapman8described 23 treated cases. Serber and his group9reported 24