The authors undertook this study to see whether highly developed coronary collaterals at an area shed by a totally occluded coronary artery predicts myocardial viability. Percutaneous coronary intervention (PCI) of a totally occluded coronary artery has been debated since its introduction. It is recommended to search for viable myocardium before opening a totally occluded coronary artery; however, there is no practical yet sensitive method of assessing myocardial viability in the catheterization laboratory. Forty-seven consecutive patients (12 women, 25.5%; 35 men, 74.5%), each with 1 totally occluded coronary artery, were prospectively enrolled to the study. After the diagnostic coronary angiography, all patients underwent dobutamine stress echocardiography to determine viable myocardium at the territory of the totally occluded coronary artery, and the status of angiographic coronary collaterals was assessed. Patients were then divided into 2 groups according to the presence (Group A) or absence (Group B) of viable myocardium by stress echocardiography. Eighteen patients (38.3%) had viable myocardium (Group A) in the area shed by the totally occluded coronary artery and 29 patients (61.7%) had nonviable myocardium (Group B). The incidences of significant coronary collateral circulation to the viable (Group A) and nonviable (Group B) areas were 66.7% (12 patients) and 20.7% (6 patients), respectively (p = 0.002). Logistic regression analysis was used to evaluate the independent factors for viable myocardium, and only significant coronary collateral circulation was found to be an independent factor for the detection of viable myocardium (p = 0.006, OR 16.7, 95% CI 2.25 to 124.4). The sensitivity and specificity of good collateral circulation for the detection of viable myocardium were 75% and 65.7%, respectively. The positive predictive and negative predictive values of the good coronary collateral circulation in detecting viable myocardium were 75% and 79%, respectively. The authors conclude that good coronary collaterals have a high sensitivity and positive predictive value for the prediction of viability as shown by dobutamine echocardiography, and only by assessing the coronary collateral circulation can one decide for percutaneous coronary revascularization, if not for coronary artery bypass surgery.