A chronic total occlusion (CTO) is defined as a completely occluded coronary artery with no antegrade flow (thrombolysis in myocardial infarction [TIMI] 0 flow) for at least three months.1 CTOs are present in 15-30 % of patients undergoing coronary angiography.2-5 In a Canadian prospective registry of 14,439 patients undergoing coronary angiography a CTO was present in 18.4 % of all patients with significant coronary artery disease (CAD).2 Approximately 1/3-1/2 6,7 of patients undergoing CTO percutaneous coronary intervention (PCI) have had a prior acute myocardial infarction (MI). This suggests acute onset of the occlusion, whereas in the remaining patients gradual development of CTO from high-grade lesions likely occurred.The basic histopathologic feature of a CTO is a proximal cap of the occlusion. This is often fibrotic or calcified and may provide considerable resistance to wire advancement during CTO PCI. Distal to the proximal cap and along the occlusion length follows a segment of loose fibrous tissue or organised thrombus, with various extent of calcification. 8,9 In several of these lesions, residual channels may be observed that are not visible under angiography. In addition, microchannels may appear during the CTO's consolidation process, however these are mostly located in the adventitia with extremely tortuous courses and do not generally traverse the entire occluded segment.10 A recent autopsy study of 95 CTO lesions from 82 patients reported frequent negative remodelling of the CTO body (more frequent with longer duration of the occlusion), very rare presence of microchannels and more frequent tapering of the distal cap as compared with the proximal cap (79 % vs. 50 %, P<0.0001). Successful CTO percutaneous coronary intervention (PCI) can significantly improve angina and improve left ventricular function. Although currently unproven, successful CTO PCI might also reduce the risk for arrhythmic events in patients with ischaemic cardiomyopathy, provide better tolerance of future acute coronary syndrome, and possibly improve survival. Evaluation by a heart team comprised of both interventional and non-interventional cardiologists and cardiac surgeons is important for determining the optimal revascularisation strategy in patients with coronary artery disease and CTOs. Ad hoc CTO PCI is generally not recommended, so as to allow sufficient time for (a) discussion with the patient about the indications, goals, risks, and alternatives to PCI; (b) careful procedural planning; and (c) contrast and radiation exposure minimisation. Use of drug-eluting stents is recommended for CTO PCI, given the lower rates of angiographic restenosis compared to bare metal stents.