Betwen January 1993 and Feruary 1993, left internal mammary arteries (İMA) of 40 consecutive patients scheduled for aorto-coronary bypass operation were examined by transthoracic B-Mode and Doppler spectrum analysis in Prof. Dr. Siyami Ersek Thoracic and Cardiovascular surgery Center. It was possible to image the IMA in all cases. External diameter of IMA at the first intercostal space was found to be 2. 93±0.05 mm by transthoracic B-Mode measurements. Peroperative measurements revealed this to be 2. 935 ± 0.05 mm. Correlation coefficient was 0.914. It is concluded that transthoracic B- Mode and Doppler spectrum analysis is an easy, cheap, safe and noninvasive technique to assess the suitability of the IMA as a bypass graft in myocardial revascularization, preoperatively . This technique may especially be valuable in patient who previously have been sumjected to median sternotomy or mediastinal irradiation and in those with generalized atherosclerotic disease, such as may be the case in diabetics.