Color Doppler-M is an echocardiographic technique which reports blood velocity along a single echocardiographic scan line at <1 mm intervals, updated every 4 to 8 ms. To investigate regional ventricular pressure gradients associated with diastolic relaxation, the authors have designed a computer system for the processing and analysis of Doppler M-mode representations of blood passing from the left atrium to the ventricle. Data were obtained digitally from a commercial echocardiographic machine with velocity output at 5-b resolution on a 0.67-mm 4-ms spatiotemporal grid. After correcting the velocity for aliasing, data were smoothed by median and Gaussian filtration to remove both random and nonrandom noise. Data extracted included peak velocity, its spatial peak, and the inertial mass of transmitral blood. Availability of these methods should allow the use of color M-mode echocardiography in the clinical and research investigation of ventricular diastolic function.