The Pressure Half-Time (PHT) method for calculating mitral valve area (MVA) was first described by Hatle and colleagues in 1979, based on the principle that the rate of equalisation of pressure between the left atrium and left ventricle during diastole is inversely proportional to the degree of mitral stenosis. The empirical constant 220 (MVA = 220/PHT) was derived from cardiac catheterisation data and validated in early echocardiographic studies. The PHT method is simple, reproducible, and operator-independent compared to the planimetry method — making it the most widely used echocardiographic tool for MVA quantification globally.