This study aims to evaluate the feasibility and diagnostic accuracy of the CART-BP ring-type wearable blood pressure monitoring device in comparison with 24-hour ambulatory blood pressure monitoring (ABPM) in patients with heart failure with reduced ejection fraction (HFrEF, LVEF ≤ 40%). As a multi-center, prospective, exploratory study, 100 patients will be enrolled at two tertiary hospitals in South Korea. The agreement between the two devices in 24-hour mean, daytime, and nighttime blood pressure measurements will be assessed per ISO 81060-2:2018 criteria.