Coronary Artery Surgery Study (CASS)

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Accession Number

Study Type
Clinical Trial

Collection Type
Open BioLINCC Study See bottom of this webpage for request information

Study Period

NHLBI Division

Dataset(s) Last Updated
July 17, 2020

Primary Publication URLs


Commercial Use Data Restrictions No

Data Restrictions Based On Area Of Research No

Available Data

Only data from the 2,099 patients selected for potential randomization are available. The full 24,959 patient registry is not included.


The Coronary Artery Surgery Study included two components, a registry of patients undergoing angiography at participating sites and a randomized trial component. The primary objective of the registry was to provide information regarding the effects of coronary artery surgery on patients with ischemic heart disease within the clinical course of treatment. The randomized component sought to evaluate the short- and long-term effects of surgical versus medical interventions in patients with a reduced ejection fraction and significant coronary artery disease.


In 1972, the National Heart and Lung Advisory Council identified the short- and long-term effects of coronary artery surgery and the patient selection criteria for surgery as topics of high priority. An Ad Hoc Policy Advisory Board on Coronary Artery Surgery was established to assist the National Heart, Lung and Blood Institute in developing a program of research activities. In August 1975, registry patients' entry and randomization began at the 11 clinical centers and coordinating center. Five additional clinical centers were added to the trial in 1976.


Patients less than 65 years of age with at least one clinical manifestation of heart disease (angina pectoris or MI) were eligible for the randomized trial if the left ventricular ejection fraction was greater than 35%, had evidence of anatomically significant coronary artery disease, the coronary artery to be bypassed supplied a viable myocardium, and at least three weeks had passed since the last myocardial infarction. The CASS registry consisted of 24,959 patients of which 2,099 were selected for potential randomization. A total 780 patients were randomized into the two arms of the trial and the remaining 1,319 patients that were medically eligible, yet non-randomized were followed for assessment of endpoints along with the randomized patients. Primary endpoints included death and myocardial infarction, and secondary endpoints included evaluation of angina and quality of life. The CASS dataset includes the 780 randomized and 1,319 medically eligible patients and approximately 17 years of follow-up for vital status. The full registry is included in the dataset.


After 8 years of follow-up, survival curves were not significantly different in the surgical and medical groups. Survival in the surgical group was significantly better for patients with three vessel disease and whose ejection fraction was between 35% and 50%. (Circulation, 1985; 72(6 pt 2):V102-9)

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Resources Available

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Study Documents

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