Abstract Background Reducing cardiovascular events arising from ostial lesions of the left circumflex artery (LCx) remains an issue following percutaneous coronary intervention (PCI) for left main disease (LMD). Despite expert consensus recommendation for the drug coated balloon (DCB) use to address it, there are concerns in using DCB following the standard practice of crossover-stenting from the left main trunk (LMT) to left anterior descending artery (LAD). Specifically, utilizing a DCB in isolation for the ostial LCx after stenting may result in additional carina shift. The combination of a conventional balloon for LMT-LAD and a DCB for LMT-LCx in KBT could potentially cause hemodynamical instability due to prolonged occlusion time for the entire left coronary artery system. Accordingly, we hypothesized the combined usage of DCB and perfusion balloon (PB) could provide a safe and effective approach for drug-eluting therapy in ostial LCx lesion. This approach aims to facilitate prolonged inflation while maintaining coronary blood flow during KBT for LMD. Purpose The aim of this study was to assess the safety and feasibility of prolonged KBT with DCB and PB for LMD. Methods In this single-center prospective observational study, we enrolled patients of de-novo LMD with ostial LCx lesion, requiring crossover stenting for the LMT-LAD followed by conventional KBT (C-KBT). IVUS-guided procedure was mandated as per the study protocol. Following confirming the achievement of optimal left main PCI by IVUS, a double-effect KBT (W-KBT) was employed. This technique involved the use of a PB for the LMT-LAD and a DCB for the LMT-LCx, sized in a 1:1 ratio to the balloons used in C-KBT. Patients in cardiogenic shock, those requiring a two-stent technique for LMD, and individuals without achievement of TIMI3 flow in the LCx after C-KBT were excluded. The primary endpoint was procedural success, defined as device delivery and balloon inflation time ≥30 sec. Secondary endpoints included the total balloon inflation time (W-KBT time), the incidence of ST-change cases, time to ST-change (ST-change time), changes in blood pressure and heart rate (delta BP and delta HR, respectively), and the frequency of inotrope usage following W-KBT. Results Between January 2023 and December 2023, 12 patients were included among 73 patients with LMD who underwent PCI during this study period. Mean age was 73.8±7.2 years (91.7% men) and median SYNTAX score was 29 (IQR: 26.3 to 34.5). The incidence of ACS was 8.3%. Procedural success was achieved in 100% of cases. The results of secondary endpoints were as follows: median W-KBT time: 60 sec (IQR: 60 to 60); the incidence of ST-change: 50% (no cases with ST-elevation); mean ST-change time: 41.2±7.1 sec; mean delta BP: -13.7±11.4 mmHg; mean delta HR: -3.4±5.9 bpm; and the use of inotrope: 0%. Conclusion Within the limited sample size of this pilot study, the safety and feasibility of the "first-in-man" technique of W-KBT were confirmed.Procedure of W-KBTStrength of W-KBT