Background/objectives: mtDNA content might be an important biomarker in heart disease prediction and to date no population studies are available on the association of mtDNA content with cardiac structure and function. We, therefore, investigated in a general population in cross-sectional and longitudinal studies whether echocardiographic indexes of LV structure and function are associated with mtDNA content measured in peripheral blood cells. Methods: At baseline we performed echocardiography in 701 randomly selected individuals (50.9% women, mean age, 53.2 years) from a Flemish population. Relative mtDNA copy number compared to nuclear DNA was measured by quantitative real-time PCR in peripheral blood cells. Results: With adjustments applied, we observed significant inverse association of LV diastolic and systolic diameters (P