Effective regurgitant orifice area (EROA) in mitral regurgitation (MR) is difficult to quantify. Clinically it is measured using the proximal isovelocity surface area (PISA) method, which is intrinsically not automatable because it requires the operator to manually identify the mitral valve orifice. This thesis explores a possible alternative to this problem. I introduce a new automated algorithm, (“AQURO”, automated quantification of regurgitant orifice area), which calculates EROA directly from echocardiographic colour M-mode data, without requiring operator input to measure the radius. Instead of measuring the distance of an isovelocity contour from the orifice, AQURO is based on a previously proposed function representing the rate of change of velocities with position upstream of the orifice (illustrated in section 1.2.3.2.4 of this thesis). I study the new automated method using three approaches: physically constructed phantom model, computational fluid dynamics, and clinical measurements in patients with mitral regurgitation. The physically constructed phantom, of Doppler Test Fluid flowing through a drilled and directly measured orifice, supported the usability of the centreline velocity profile in this way for quantification of the orifice area. The computational model showed that the AQURO principle of a predictable progressive decline in velocity along the centreline appears to be valid over a range of positions in the left ventricle. The clinical measurements in patients with mitral regurgitation showed a good agreement between measurements of EROA using AQURO, which is found to be faster and have higher reproducibility than conventional PISA. I conclude that the colour M-mode centreline velocity profile is an efficient way of extracting information about mitral EROA. By eliminating the need to identify the orifice location, AQURO avoids an important source of measurement variability. Compared with PISA, it also reduces the analysis time allowing analysis and averaging of data from significantly more beats, improving the consistency of EROA quantification. If my findings are reproduced in independent laboratories, AQURO, being fully automated, would be a simple, effective enhancement for EROA quantification using standard echocardiographic equipment.