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Background Lower exercise capacity, as measured by 6-minute walk distance (6MWD), is associated with incident heart failure (HF). Among those without HF, the associations of measures of cardiac function with 6MWD are unclear, and may provide insight regarding the risk of incident HF. Objectives The purpose of this study was to understand the relationships between cardiac function and exercise capacity. Methods This study evaluated the associations of cardiac mechanics with 6MWD in the sixth examination of the Multi-Ethnic Study of Atherosclerosis. Echocardiography (2-dimensional, Doppler, and speckle-tracking) was performed at rest and after passive leg raise to evaluate functional reserve after intravascular volume challenge. Results Of 2,096 participants without HF (mean age 73 years, 48% men, 58% non-White), individuals with lower (worse) left atrial (LA) reservoir strain were older and had higher blood pressure. Lower resting LA reservoir strain (β coefficient per SD decrease: −5.0; 95% confidence interval [CI]: −8.8 to −1.3 m; p = 0.009), inability to augment LA reservoir strain after passive leg raise (β coefficient per SD decrease: −5.8; 95% CI: −9.1 to −2.5 m; p Conclusions Among individuals without HF, worse biatrial function, lack of LA functional reserve, and worse LV diastolic function were associated with reduced submaximal exercise capacity. Therapies aimed to improve these functional domains may increase exercise capacity and prevent HF.