SUMMARY. M-mode echocardiographic, hemodynamic, and angiographic correlations are presented for 97 patients with d-transposition of the great arteries. Forty-one patients were Studied before and 73 patients after the Mustard operation; 17 patients were studied sequentially before and after the Mustard operation. The echocardiographic diagnosis of d-transposition Could be made with high accuracy by using two criteria: (1) opening of the posterior semilunar Valve earlier than the anterior semilunar valve, and (2) location of the anterior semilunar valve to the right of the posterior semilunar valve with transducer angulation toward the right shoulder. In the pre-Mustard group the presence of associated lesions such as patent ductus arteriosus and Ventricular septal defect was suggested by an elevated left ventricular end-diastolic/right ventricular end-diastolic dimension ratio (> 1.2). In the post-Mustard group, after correction of shunting lesions, this ratio was similar to that in patients with intact ventricular septum. In preMustard patients the anatomically fixed type of left ventricular outflow tract stenosis was SUggested by a left ventricular outflow tract/pulmonary artery ratio of less than 0.5. This ratio Was 0.52 • 0.1 in those in whom resection of the anatomic stenosis and Mustard operation were Performed. Right ventricular function could be assessed by the pre-ejection period/right ventricular ejection time ratio; a ratio of greater than 0.5 was associated with angiographically determined ejection fraction of 0.5 or less.It is suggested that M-mode echocardiography provides a reliable means for the diagnosis of dtransposition of the great arteries as well as the quantitative and qualitative assessment of associated lesions.KEy WORDS: Echocardiography in transposition m Dynamic stenosis in transposition Echocardiographic diagnosis of transposition M-mode echocardiography has proved to be a reliable means for the diagnosis of d-transposition of the great arteries [8,5]. The M-mode echocardiographic diagnostic criteria are the demonstration of (1) an anterior aorta, identified by opening of the anterior semilunar valve after the posterior semilunar valve, and (2) tion of the aortic root relative to the pulmonary artery root. Associated lesions such as left ventricular outflow tract stenosis can be qualitatively and quantitatively evaluated [3,12]. Echocardiographic assessments of pulmonary artery 110, 11] and left ventricular pressure [13] have also been reported, but the clinical reliability of these criteria is yet to be tested. The purpose of this study was to evaluate the diagnostic usefulness of various echocardiographic parameters and to present their hemodynamic correlates, both before and after the Mustard operation and correction of associated lesions.