The goals of the present study were to develop and validate a computer-assisted, video-based image processing (CAVIP) system to measure time-dependent changes in isolated myocyte geometry during contraction and to use the CAVIP system to examine spatial characteristics of the myocyte during contraction in normal myocytes and in myocytes after development of dilated cardiomyopathy (DCM). Myocytes were isolated from the left ventricles of five control pigs and five pigs that developed chronic tachycardia (240 beats/min; 3 wk)-induced DCM. Isolated myocytes were stimulated and recorded using a high-speed camera interfaced with a standard video recording system. There was a significant linear relation between the indexes of time-dependent changes in myocyte length as measured by a conventional video edge-detector system and by the CAVIP system (r > 0.96; P < 0.01). After this validation procedure, dynamic changes in myocyte width and profile area with DCM were examined. Myocyte resting profile area was 33% larger in DCM myocytes compared with controls. However, there was no difference in the rate of area change with contraction between the two groups. Percent changes in myocyte width and profile area at peak contraction were significantly lower in the DCM group (43 and 46% respectively, P < 0.05). Therefore, the present study demonstrated that the CAVIP system provides unique information on time-dependent changes in myocyte geometry during contraction, particularly with the development of cardiomyopathic disease.