BQ-123 is a selective endothelin A (ETA) receptor antagonist widely used in research to study the role of endothelin-1 in various physiological and pathological processes. It is primarily applied in cardiovascular research due to its ability to block ETA-mediated vasoconstriction, helping investigate conditions such as hypertension, pulmonary arterial hypertension, and vascular remodeling. In experimental models, BQ-123 has demonstrated protective effects in ischemia-reperfusion injury, particularly in the heart and brain, by improving blood flow and reducing tissue damage. It is also used to explore the involvement of endothelin signaling in cancer progression, as ETA activation has been linked to tumor cell proliferation and invasion in certain cancers. Due to its specificity for ETA receptors over ETB, BQ-123 serves as a valuable tool for dissecting receptor-specific effects of endothelin, making it important in pharmacological studies aiming to develop targeted therapies for vascular and inflammatory diseases.