Jugular venous distension (JVD) is the visible distension of the external or internal jugular veins, reflecting elevated central venous pressure (CVP) and right atrial pressure. The internal jugular vein (IJV) is preferred for assessment because it connects directly to the superior vena cava and right atrium without intervening valves, making it a reliable manometer of right heart pressures. With the patient positioned at 45 degrees, the vertical height of the jugular venous pulsation above the sternal angle is measured. Adding 5 cm (the fixed anatomical distance from the sternal angle to the center of the right atrium regardless of patient position) gives the estimated CVP in cm H2O. Normal JVP is less than 8 cm H2O (or less than 3-4 cm above the sternal angle at 45 degrees). Elevated JVP occurs from increased right atrial pressure caused by: right ventricular failure (cor pulmonale, right-sided MI), biventricular heart failure, volume overload, tricuspid regurgitation (large v waves), tricuspid stenosis (large a waves), cardiac tamponade (elevated JVP with Kussmaul sign -- JVP rises with inspiration instead of falling), constrictive pericarditis, superior vena cava...