Left ventricular (LV) filling results from diastolic suction of the left ventricle and passive left atrial (LA) emptying at early diastole and LA contraction at end-diastole. Effects of aging on LA and LV geometric characteristics and function and its consequences for LV filling are incompletely understood. Insight into these effects may increase the understanding of diastolic function. Cardiac magnetic resonance imaging was used to study effects of aging on left atrioventricular coupling and LV filling. Forty healthy volunteers underwent cardiac magnetic resonance imaging and were subdivided into 2 age groups of 20 to 40 (younger group) and 40 to 65 years (older group). For the older group, LA volumes were larger (p <0.05) and LV volumes, including stroke volumes, were smaller (p <0.05), whereas ejection fraction remained constant. LA/LV volume ratios were larger (0.27 ± 0.06 vs 0.19 ± 0.03; p <0.001) and correlated with LV mass–volume ratio (r = 0.42, p <0.01). The older group also had lower LA passive emptying (15 ± 3.0 vs 19 ± 4.8 ml/m²; p <0.05) and higher LA active emptying volumes (13 ± 3.1 vs 11 ± 3.9 ml/m²; p <0.05). For both groups, conduit volume contributed most to LV filling, but was lower in the older group (21 ± 5.1 vs 27 ± 9.0 ml; p <0.05). In conclusion, changes in LA volume and function were age dependent and related to changes in LV mass–volume ratio. Conduit volume contributed most to LV filling and decreased with age, suggesting it to be an indicator of diastolic function.