The goal of this prospective observational study is to learn about in patients who need percutaneous coronary intervention for coronary artery disease. The main questions it aims to answer are:

• Fractional flow reserve according to coronary angiography findings after coronary artery balloon angioplasty
• Differences in fractional blood flow reserve before and after lesions between coronary balloon angioplasty using a scoring balloon and a regular balloon Participants will voluntarily consent to the study after being fully informed about the study and given ample opportunity to ask questions.

Inclusion Criteria:

• Patients with clinically stable coronary artery disease
• Patients undergoing balloon angioplasty as an interventional procedure (FFR-guided PCI) using coronary artery fractional blood flow reserve for de novo lesions with a standard vessel diameter of 2.25 mm or more under percutaneous coronary angiography (hereafter referred to as coronary angiography)

(Note) If there are other lesions in the proximal area and the FFR of the distal lesion is collected, it is included in the selection target regardless of whether or not the proximal lesion was operated on.

Exclusion Criteria:

• Target lesion with stenosis of less than 50% or greater than 90% of the internal diameter
• Procedure for restenosis within the stent
• Pre-dilation performed on the target lesion before the coronary artery fractional blood flow reserve test
• Prior coronary artery bypass surgery
• Clinically unstable or ST-segment elevation myocardial infarction
• Myocardial infarction in the region supplied by the target vessel
• Target vessel is a blood vessel that supplies collateral circulation for occlusion of other blood vessels (not applicable when the need for collateral circulation has been resolved due to the opening of another vessel occlusion)
• Left ventricular ejection fraction (EF) less than 30%
• Most recently measured eGFR is less than 30 right before the procedure
• Accompanying primary valve disease requiring treatment
• Accompanying primary heart disease such as dilated cardiomyopathy, hypertrophic cardiomyopathy, or restrictive cardiomyopathy
• Congenital heart disease

Patients who met the inclusion criteria and underwent interventions, as determined by clinical necessity, using fractional blood flow reserve (FFR) after percutaneous coronary angiography (PCA) will be included in the study.