AbstractLeft ventricular internal dimensions, septal and posterior wall thickness, aortic root diameter, and left atrial dimensions, were independently measured by two experienced interpreters on 50 consecutive routinely performed M‐mode echocardiograms. The purpose of this work was to evaluate the reproducibility of these measurements and to assess if a different “diagnostic effect” could be provided by the two readers. The extent of interobserver variability was calculated and expressed as a percent of the mean. No significant interobserver variability was found for all the measured echocardiographic parameters and the two interpreters gave rise to the same “diagnostic effects.” Therefore, the authors suggest following well stated guidelines to provide uniformity in the process of determining the boundaries of the structures to be measured and adjusting the actual measurements by multiplying by a conversion factor (representing the ratio between the number of 1 cm markers and the distance in centimeters between the first and the last marker), as opposed to interpolating between the marks on the recording paper.