AbstractThe general objective of this study was to develop a noninva‐sive method for efficiently and reproducibly determining relative cardiac function parameters in the chick embryo. The specific objectives of the study were 1) to develop several methods for computer‐assisted image processing and quan‐titation of relative intraventricular blood volumes in the 3‐day‐old embryonic chick heart and 2) to compare methods for precision and with a previously established manual processing method. Images of the embryonic chick heart in ovo were recorded on videocassette tape, digitized, and enhanced by computer‐aided histogram equalization. The area occupied by blood within the common ventricle was extracted by region‐growing and spurious region removal algorithms and defined by the determination of edge‐pixel coordinates. Edge‐pixel coordinates of the longitudinal and transverse axes of the common ventricular blood region were located by three different methods, the lengths of the axes calculated, and volumes computed from the equation for determining volume of a prolate spheroid. Twenty‐five images of the embryonic heart were randomly selected and processed. Volumes were calculated with each of the three methods on six different occasions. A coefficient of variation was determined for each image by each of the three methods. A mean coefficient of variation was calculated for each method. The intraobserver mean coefficient of variation for each method was 7.4%. When a 2‐way ANOVA was conducted, mean coefficients of variation did not differ significantly for the three methods. However, computer processing (in addition to significantly reducing the time required to generate data) reduced the coefficient of variation observed in manual processing by 56.5%.