The article discusses the diagnostic challenges in identifying supraventricular tachycardia (SVT) with narrow QRS complexes, focusing on differentiating between atrial tachycardia (AT), orthodromic reciprocating tachycardia (ORT), and atrioventricular nodal reentrant tachycardia (AVNRT). The authors propose a systematic approach, termed "SVT Quest," involving three steps to improve diagnostic accuracy. Step 1 involves differentiating AT from ORT and AVNRT using various diagnostic maneuvers, such as the V-A-V or V-A-A-V response after right ventricular overdrive pacing (VOP), the ΔAA interval, and differential atrial overdrive pacing. These maneuvers help identify the presence of retrograde conduction and assess the conduction pathways involved. Step 2 focuses on differentiating ORT from AVNRT using techniques like para-Hisian pacing, a scanned single ventricular extrastimulus during His-bundle refractoriness, and the postpacing interval (PPI) minus tachycardia cycle length (TCL). These methods help determine the conduction pathways and identify the presence of an accessory pathway or nodal pathway. Step 3 characterizes concealed nodoventricular/nodofascicular (NV/NF) pathways and His-ventricular (HV) pathway-related tachycardia using observations such as the V-V-A response, Δ atrioHis interval, and paradoxical reset phenomenon. These maneuvers help identify the specific conduction pathways involved in the tachycardia. The article emphasizes the importance of using multiple diagnostic maneuvers in combination to improve diagnostic accuracy and avoid misdiagnosis. It also highlights the challenges in differentiating between various SVT mechanisms, particularly in cases involving concealed pathways. The authors conclude that a comprehensive understanding of these diagnostic techniques is essential for accurate diagnosis and appropriate treatment of SVT with narrow QRS complexes.The article discusses the diagnostic challenges in identifying supraventricular tachycardia (SVT) with narrow QRS complexes, focusing on differentiating between atrial tachycardia (AT), orthodromic reciprocating tachycardia (ORT), and atrioventricular nodal reentrant tachycardia (AVNRT). The authors propose a systematic approach, termed "SVT Quest," involving three steps to improve diagnostic accuracy. Step 1 involves differentiating AT from ORT and AVNRT using various diagnostic maneuvers, such as the V-A-V or V-A-A-V response after right ventricular overdrive pacing (VOP), the ΔAA interval, and differential atrial overdrive pacing. These maneuvers help identify the presence of retrograde conduction and assess the conduction pathways involved. Step 2 focuses on differentiating ORT from AVNRT using techniques like para-Hisian pacing, a scanned single ventricular extrastimulus during His-bundle refractoriness, and the postpacing interval (PPI) minus tachycardia cycle length (TCL). These methods help determine the conduction pathways and identify the presence of an accessory pathway or nodal pathway. Step 3 characterizes concealed nodoventricular/nodofascicular (NV/NF) pathways and His-ventricular (HV) pathway-related tachycardia using observations such as the V-V-A response, Δ atrioHis interval, and paradoxical reset phenomenon. These maneuvers help identify the specific conduction pathways involved in the tachycardia. The article emphasizes the importance of using multiple diagnostic maneuvers in combination to improve diagnostic accuracy and avoid misdiagnosis. It also highlights the challenges in differentiating between various SVT mechanisms, particularly in cases involving concealed pathways. The authors conclude that a comprehensive understanding of these diagnostic techniques is essential for accurate diagnosis and appropriate treatment of SVT with narrow QRS complexes.