Functional myocardial changes which result from ischemia are typically local rather than total. For assessing such regional changes quantitatively, left ventricular angiography has been used. The ventricular image has been divided into several components which can be measured individually. In order to test the validity of such methods, left ventricles of 5 dogs were labeled with endocardial tantalum markers and the segmental myocardial motion was estimated using cineangiography. Variance analysis of beat to beat measurements of total ejection fractions was performed. Total ejection fraction demonstrated the least variation with an average 3.5 per cent, segmental myocardial shortening 15 and regional stroke volumes 13 to 18 per cent. Intermethodologic variation with different regional volume measurements was 11 to 13 per cent. Regional stroke volume calculations showed large methodologic variations in beat to beat analysis. Conclusions and clinical decisions based on such measurements should be drawn with caution.