BACKGROUND: Transthyretin amyloid cardiomyopathy (ATTR-CM) affects all cardiac chambers to cause left ventricular (LV) deformation as well as left atrial (LA) remodeling and functional impairment. We investigated the associations of the LA volume index (LAVI):LV ejection fraction (LVEF) ratio with the increased risk of death, heart transplant, or LV assist device implantation (LVAD) in patients with ATTR-CM. METHODS: This was a retrospective cohort study involving 69 heart failure (HF) patients with ATTR-CM at an academic medical center between 1 November 2008 and 31 March 2024. ATTR-CM was diagnosed using a technetium-diphosphonate/pyrophosphate scan or an endomyocardial biopsy. The LAVI and LVEF were measured by echocardiography. Cox proportional hazards models were used for the analysis. RESULTS: The mean (SD) age of the participants was 77.5 (9.3) years. Over a median (IQR) follow-up period of 1.96 (0.67-2.82) years, we observed 24 composite events that included twenty-two deaths, two heart transplants, and two LVAD implantations (who subsequently died). In multivariable-adjusted analyses that accounted for age and the glomerular filtration rate, a one-unit increase in the LAVI:LVEF ratio was associated with a doubling of the risk (HR, 95% CI: 2.06, 1.11-3.82) of experiencing the composite outcome. CONCLUSIONS: A one-unit increase in the LAVI:LVEF ratio was associated with an increased risk of death, heart transplant, or LVAD implantation in patients with ATTR-CM.