The left atrium enlarges in association with many factors, including aging, atrial fibrillation, hypertension, diastolic dysfunction, and heart failure (HF) with low ejection fraction. However, left atrial (LA) volume, geometry, and emptying have not been compared between diastolic and systolic HF, nor has the association of LA volume for new HF been determined in older subjects, many of whom have normal ejection fraction. We used echocardiography to measure the LA volume, geometry, and emptying in 851 community-dwelling subjects > or =65 years of age, including 180 with HF at baseline and 255 participants who subsequently developed HF. The LA volume, area, and linear dimensions were higher in the prevalent and incident HF groups than in controls and did not differ between those with systolic versus diastolic HF, independent of co-morbidities and Doppler measures of diastolic function. The fractional area change was associated with prevalent, but not incident, HF. In conclusion, in population-based older subjects, the LA size is increased and LA emptying decreased in patients with either systolic or diastolic HF. LA size is associated with the new development of HF. These findings highlight the important role of the left atrium in HF, with or without a decreased ejection fraction.