1. Ultrasonic image processing method comprising steps of: acquiring ultrasonic signals related to an object in a medium, said object having moving parts submitted to periodic dilation related to a substantially regular time cycle, constructing an ultrasonic grayscale 2-D image sequence (A) representing a cross-section of a segment of said object having a longitudinal axis (X) perpendicular to the grayscale image lines (Z), constructing a dilation curve image (B), related to the dilation of said moving parts along a grayscale image line, in function of time instants (n) of a time cycle, and coupling the dilation curve to the grayscale image line, and constructing a first movable pattern (AP) on the grayscale image (A), denoted first image, to indicate a grayscale image line, so as to automatically generate the construction of an image (B) of a coupled dilation curve (&Dgr;(X,n)), denoted second image, and displaying a composite image sequence wherein an image includes a grayscale image (A) with the first movable pattern (AP) indicating a grayscale image line location (X) and the dilation curve of the second image (B) related to said first pattern location (X).