twodimensional echocardiographic left atrialtoaortic ratio in healthy adult dogs a reexamination of reference intervals introduction left atrialtoaortic ratios laao provide a body weight independent estimate of left atrial size however reference intervals were established with small sample populations and for only single points in the cardiac cycle more robust reference intervals are warrantedanimals two hundred and thirty eight apparently healthy adult dogsmaterials and methods laao measurements were obtained at 3 points in the cardiac cycle maximal dimension at the closing of the aortic valve or just before opening of the mitral valve laaomax minimal dimension at the onset of the qrs complex laaomin and at the onset of atrial systole laaop laaomax was obtained from right parasternal short and longaxis views and laaomin and laaop were obtained from the right parasternal shortaxis view dogs were excluded from analyses of reference intervals if weightbased left atrial and left ventricular diastolic dimensions exceeded reference interval limits effects of breed and body weight on laao measurements were examinedresults upper laao reference limits mostly agreed with previously published limits although 10 of dogs had laaomax in the shortaxis view exceeding 16 these dogs had smaller aortae than expected for their body weight and included mostly boxers and english setters reference limits for laaomin and laaop were smaller than those for laaomax in either view no laao measurements were associated with body weightconclusions reference limits were either confirmed or established for the common twodimensional methods of assessing relative left atrial size in healthy dogs clinicians should use caution when diagnosing mild left atrial enlargement in certain dog breeds and should examine the weightbased aortic dimensions in such cases