Background: Impairment of left ventricular (LV) longitudinal function is an early marker of systolic dysfunction in hypertrophic cardiomyopathy (HCM). Longitudinal function can be assessed using mitral annular plane systolic excursion (MAPSE) and strain; however, these require left apical views that can be challenging to acquire in cats. Aortic annular plane systolic excursion (AAPSE), obtained from a right parasternal short-axis view (RPSA), is a measure of LV longitudinal function that correlates with MAPSE and strain in people. Hypothesis: AAPSE is lower in cats with HCM compared to control cats, and cats in stage C have the lowest AAPSE. Animals: One-hundred and seventy-five cats: 60 normal, 61 HCM stage B and 54 HCM stage C cats. Materials: Multicenter retrospective study. HCM was defined as LV wall thickness ≥6 mm. M-mode bisecting the aorta in RPSA was used to measure AAPSE. Results: AAPSE was lower in HCM cats compared to normal cats and was lowest in HCM stage C. An AAPSE <2.9 mm gave a sensitivity of 83% (95% CI 71% - 91%) and specificity of 92% (95% CI 82% - 97%) to differentiate HCM stage C from stage B. AAPSE correlated with measures of LV longitudinal function, and atrial function, but showed no correlation with LV fractional shortening. AAPSE showed excellent intra- and inter-observer reliability. Conclusions and clinical importance: AAPSE is an easily acquired echocardiographic variable that was reduced in HCM and was lowest in stage C. This might be a new measurement of LV systolic performance in cats with HCM.