A1. In WT, systolic diameter increases with age and is significantly larger in 2 yr old WT compared to 2 mo. Systolic diameter in D3KO is not significantly different from age-matched WT. A2. In WT, diastolic diameter slightly increases with age and is significantly larger in 1 yr old WT compared to 2 mo old D3KO. Diastolic diameter in D3KO is not significantly different from age-matched WT. B1. In WT, systolic volume increases with age and is significantly larger in the 2 yr WT compared to the 2 mo old WT, but systolic volumes of age-matched WT and D3KO are similar. B2. In WT, diastolic volume increases with age and is significantly larger in 1 yr old WT over 2 mo, but diastolic volumes of young WT and D3KO are similar. C1. Left ventricle (LV) mass increases with age in WT and is significantly larger in 1 and 2 yr old WT compared to 2 mo old WT; however, LV masses between age-matched WT and D3KO are not significantly different. C2. In WT, LV mass adjusted for body weight remains stable with age but is significantly decreased in 2 mo old D3KO compared to 2 yr and 2 mo old WT.