Inclusion Criteria:
* ≥ 19 years of age
* Patients with in-stent restenosis who are candidates for percutaneous coronary intervention (PCI)
* In cases corresponding to one of the following conditions: non-ST-segment elevation myocardial infarction (NSTEMI), stable angina, unstable angina, or silent myocardial ischemia
* Women of childbearing potential\* must agree to use at least one medically acceptable method of contraception\*\* throughout the duration of the clinical trial
* Subjects who voluntarily agree to participate and provide written informed consent
* Subjects who are willing to comply with the requirements of the clinical trial protocol
* Subjects who develop in-stent restenosis (ISR) ≥ 90 days after the index coronary stent implantation, with the restenosis classified as Mehran type I to III
* Subjects with a maximum of two ISR lesions, with visually estimated significant coronary artery stenosis on quantitative coronary angiography analysis (QCA) meeting one of the following criteria:
1. In asymptomatic patients: in-segment percent diameter stenosis (DS%) \> 70% compared to the reference vessel diameter of the target vessel\* (\*Target vessel: the vessel containing the target lesion with the minimum lumen diameter.)
2. In patients with angina symptoms or evidence of ischemia on non-invasive functional testing: DS% \> 50%
* On QCA, the ISR lesion(s) to be treated must have a lesion length \< 36 mm and the reference vessel diameter (RVD) of the target coronary artery must be between 2.0 mm and 4.0 mm.
Exclusion Criteria:
* Patients diagnosed with ST-segment elevation myocardial infarction (STEMI) by electrocardiogram.
* Known hypersensitivity or contraindications at screening to any of the following drugs or substances: Aspirin, Heparin, Clopidogrel, Prasugrel, Ticagrelor, Sirolimus, Paclitaxel, Delivery matrix (e.g., shellac, vitamin E-TPGS), Ticlopidine, Contrast agents (e.g., Iopromide) Note: Subjects with contrast media sensitivity may be enrolled if the reaction is manageable with steroids and pheniramine; however, those with a known anaphylactic reaction are excluded.
* Subjects who are scheduled for or require surgery within 1 year of the index procedure that would necessitate discontinuation of antiplatelet therapy.
* Subjects with bleeding disorders, gastrointestinal ulcers, or any conditions that may increase the risk of bleeding, in which anticoagulation is contraindicated or limited.
* Subjects with a left ventricular ejection fraction (LVEF) \< 30% as assessed by echocardiography.
* Severe renal failure (Creatinine \> 2.0 mg/dL) that makes QCA inappropriate.
* Subjects with cardiogenic shock.
* Pregnant or breastfeeding women: Women of childbearing potential with a positive urine hCG (or serum β-hCG) test are excluded.
* Subjects with an estimated life expectancy of less than 1 year due to comorbid conditions.
* Subjects with medical conditions such as significant psychiatric disorders that may interfere with trial participation or outcomes.
* Subjects who, in the investigator's opinion, are inappropriate for this clinical trial or for whom participation poses increased risk.
* Participation in another clinical trial currently or within 90 days prior to screening.
* Any other condition deemed ethically or clinically inappropriate by the investigator to participate in the study: Specific reasons should be recorded in the Case Report Form (CRF).
\[Exclusion Criteria Based on QCA and Pre-Dilatation Assessment of ISR Lesions\]
* ISR lesions located in graft vessels following coronary artery bypass grafting (CABG).
* Presence of coronary stent fracture in the ISR lesion to be treated.
* Target lesion with two or more stents implanted, i.e., all segments of the target lesion contain ≥2 layers of stents.
* Presence of additional lesions proximal or clinically significant distal to the target lesion (\>2.0 mm RVD) with \>50% stenosis.
* Subjects requiring CABG based on any of the following:
1. Lesions in the left main coronary artery.
2. Triple-vessel coronary artery disease.
3. Other conditions requiring CABG as determined by the investigator.
* Subjects for whom pre-dilatation is not feasible or has failed, making application of the investigational device difficult due to any of the following:
1. Total occlusion of the target lesion.
2. Evidence of thrombus not treatable with aspiration.
3. Severe vessel tortuosity or calcification preventing access to the target site, as determined by the investigator.
4. Other conditions deemed unsuitable for investigational device application by the investigator.
* After lesion pre-dilatation, if any of the following are present:
1. Need for atherectomy (rotational, orbital, or laser).
2. Presence of flow-limiting dissection of NHLBI type C or higher requiring stent implantation.
3. Residual stenosis\* in the target lesion. (\*Defined as in-segment DS \> 30%)
4. Fractional flow reserve (FFR) ≤ 0.8 (FFR measurement may be omitted at the discretion of the investigator.)
5. TIMI flow \< 3
