At present there are two recognised guidelines for the echocardiographic assessment of left ventricular diastolic function provided by the British Society of Echocardiography and American Society of Echocardiography/European Association of Cardiovascular Imaging. However, no direct comparison of these guidelines has been performed to establish whether they provide similar diastolic grading. One hundred and eighty-nine consecutive patients in sinus rhythm who underwent transthoracic echocardiography for a primary indication of either heart failure assessment or assessment of left ventricular systolic function were extracted from our database (McKesson Cardiology). Left ventricular diastolic function assessment was performed using both guidelines and the results were compared. Chi-square, Kappa score and one-way ANOVA were used to evaluate the data at a level of P < 0.05. The most frequent outcome was unclassifiable diastolic function with significantly more patients being labelled unclassified with the British compared to American guidelines (47.4 vs 20.5%, P < 0.0001). Having excluded all unclassifiable patients, a significant difference still existed between the two guidelines with a higher proportion of grade one outcomes awarded by the ASE/EACVI guidelines. When grading subcategories were individually compared, there was significantly more grade one diastolic gradings awarded by American compared to the British guidelines (40.7 vs 20.1%, P < 0.0001). In 47% of patients it was not possible to grade diastolic function using the British guidelines, compared to 21% using the American guidelines. For those patients where grading was possible, there was a significant difference in patients classified with normal and grade one diastolic function when using British and American guidelines.