<p>Percutaneous coronary intervention (PCI) has evolved significantly with technological advances, allowing for higher procedural success rates and improved patient outcomes. However, the growing complexity of cases involving severely calcified lesions, tortuous vessels, and chronic total occlusions has increased procedural challenges. In such scenarios, the guide extension catheter (GEC, or guiding catheter extension) plays a critical role by enhancing device passage and providing additional backup support, making it indispensable in modern PCI. Various types of GECs offer distinct characteristics that influence their selection based on lesion type, device compatibility, and procedural requirements. The GEC is used for multiple purposes, including backup support, deep engagement, imaging device insertion, stent protection, thrombectomy, and foreign body removal. Despite its utility, GEC use is associated with potential complications, including vessel injury, thrombosis, air embolism, and hemodynamic instability. Careful technique and proper selection are critical to minimizing risks. Overall, the GEC is an essential tool in complex PCI procedures, offering significant advantages in improving procedural success.</p> Graphical abstract <p>Guide extension catheters in coronary intervention. <i>GEC</i> guide extension catheter, <i>IVUS</i> intravascular ultrasound, <i>OAS</i> orbital atherectomy, <i>OCT</i> optical coherence tomography, <i>ROTA</i> rotational atherectomy. Some of the methods shown involve off-label use; however, such use is not being recommended. Off-label use should be performed only by experienced operators and only when no alternative options are available in procedure. Always refer to the usage instructions.</p> <p></p>