WITH the advent of cardiac catheterization and operative procedures for correction of valvular deformities it has become increasingly important for the pathologist to attempt, from post-mortem examination, a more accurate estimation of the in vivo performance of the heart. The few measurements taken routinely in the past have proved of limited value in the interpretation of cardiac function during life. The present communication reports initial efforts to develop and standardize a procedure of post-mortem valvular examination that can be correlated with in vivo studies of cardiac function. For this purpose resistance to flow through the various heart valves was measured . . .