The occlusion of a coronary artery does not necessarily imply the existence of nonviable myocardium of that flow-dependent region, because the presence of a well developed collateral circulation may be a sufficient nutrient source. During an episode of increased demand for myocardial oxygen, this collateral blood supply may become insufficient, and symptoms of myocardial ischemia may arise. PTCA of the occluded vessel appears to be an attractive approach to relieve ischemia in this situation. The primary success of dilatation of totally occluded segments depends largely on the duration of the occlusion but also on anatomic factors such as total or functional occlusion, the length of the occluded segment, and good angiographic visualization of the coronary artery distal to the occlusion by collaterals. The primary success rate (+/- 60%) of PTCA of occluded vessels is lower than the success rate (greater than 90%) of PTCA of nonocclusive stenoses. Also the restenosis rate (+/- 40%) and subsequent recurrence rate of angina pectoris is higher, compared to the 30% restenosis rate after dilatation of conventional lesions. Newer percutaneous techniques such as lasers, newly designed guide wires, and intravascular imaging devices are necessary to increase the primary success rate. Whether these techniques will also improve the long-term results remains uncertain.