he incidence of coronary artery perforation (CAP) and/or tamponade in patients undergoing percutaneous coronary interventions (PCI) is proportional to the complexity of the procedure, ranging from 0.2-0.4% in non-complex lesions, 1,2 to 1.4-4.1% in chronic total occlusions (CTO). 3,4 In contemporary registries the 1-year all-cause mortality after CAP is 18-35%, which is 2-3-fold higher than in patients without CAP. 2,5-9 Predictors of CAP have been found to be age, female sex, atherectomy devices, hydrophilic wires, oversized balloons and/or stents, and excessive post dilations, as well as complex procedures such as calcified lesions, previous coronary artery bypass grafting (CABG), and CTO. 2,5,8-10 Perforations based on their angiographic appearance were classified by Ellis et al into tree classes. 11 However, this risk stratification may be insufficient because almost 21-25% of CAP cases are not recognized during the procedure, but afterwards in the ward as tamponade. 2,5 A fatal outcome of CAP directly correlates with development of tamponade and concurrent arrhythmias with a high need for emergency pericardiocentesis. 2,9 There may be differences in the clinical presentation, because a perforation with acute tamponade is likely caused by oversized balloons and a stent in the proximal arteries, whereas distal perforations are likely caused by distal guidewire exits in smaller arteries and many are missed in the catheter laboratory (cath-lab) only to be disclosed as late tamponade in the ward. It is unknown if there are differences in outcomes between acute and late tamponade after a perforation. We report the incidence, risk factors, and short-and long-term (12 years) outcomes of CAP from the perspective of clinical relevance depending on the occurrence of a perforation and whether it was accompanied by acute or late tamponade. Methods Data were collected between 1 May 2005 and 23 January 2017 from the Swedish Coronary Angiography and Angioplasty Register (SCAAR), which is an integrated part of the Swedish Web-system for Enhancement and Development of Evidence-based care in Heart Disease Evaluated According to Recommended Therapies (SWEDEHEART), with at least 1 year of follow-up. Data in the SCAAR are recorded online through a web interface for all consecutive patient data from every center (n=30) performing PCI in