Ten closed-chested beagles were employed to determine whether reproducible echocontrast imaging of the myocardium could be obtained following injection of the new ultrasonic contrast medium Echocon into the aortic root, and whether myocardial perfusion defects could be successfully diagnosed by this method. The change in intensity of contrast in the myocardium was measured by videodensitometry simultaneously in the supply areas of the left anterior descending and left circumflex branches of the left coronary artery before and during occlusion of the circumflex branch by means of a balloon catheter. Injection of Echocon into the aortic root led to reproducible echocontrast imaging of the entire myocardium. The occlusion of the circumflex branch caused a significant reduction (p less than 0.01) in intensity of contrast in the supply area of the circumflex branch, whereas no differences by comparison with the starting values were identifiable in the supply area of the left anterior descending branch. The correlation factor between the sizes of the perfusion defects ascertained by echocardiography and by planimetric measurement using a pathological anatomical approach was found to be r = 0.89. The injection of Echocon into the aortic root did not induce any significant changes in the aortic or pulmonary pressure, or in heart rate. Only slight flattening of the T-waves, which never lasted longer than 15 seconds, was observed in 50% of the animals. Contrast echocardiography of the myocardium could thus contribute to the diagnosis of coronary heart disease, i.e. perfusion defects.