The study aimed to assess interobserver variability in M-mode echocardiographic measurements and to determine the need for standardization. Four hundred M-mode echocardiographic surveys were distributed, and 76 responses were received, allowing for the comparison of measurement criteria and interobserver variability. The results showed significant variability in measurements, particularly for structures like the right ventricular wall and cavity, with percent uncertainties ranging from 10% to 80%. The study recommended standardized criteria for measurement, such as measuring the aortic root at the onset of the first rapid deflection of the QRS complex, and using the onset of the QRS for end-diastole measurements. The recommendations also emphasized the importance of consistent methodology and quality control to improve the reproducibility of M-mode echocardiographic measurements.The study aimed to assess interobserver variability in M-mode echocardiographic measurements and to determine the need for standardization. Four hundred M-mode echocardiographic surveys were distributed, and 76 responses were received, allowing for the comparison of measurement criteria and interobserver variability. The results showed significant variability in measurements, particularly for structures like the right ventricular wall and cavity, with percent uncertainties ranging from 10% to 80%. The study recommended standardized criteria for measurement, such as measuring the aortic root at the onset of the first rapid deflection of the QRS complex, and using the onset of the QRS for end-diastole measurements. The recommendations also emphasized the importance of consistent methodology and quality control to improve the reproducibility of M-mode echocardiographic measurements.