Sodium nitrate (NaNO3) supplementation has been shown to protect against the development of hypertension-mediated heart failure, reverse age-related diastolic dysfunction and improve in vitro cardiac contractility. While the mechanism(s) remain unclear, in skeletal muscle, the consumption of nitrate has been shown to increase mitochondrial coupling efficiency. Intriguingly, impairments in mitochondrial bioenergetics have been associated with heart failure, and therefore, the present thesis aimed to determine the influence of NaNO3 on mitochondrial bioenergetics in the left ventricle. To achieve this, Sprague-Dawley rats were provided water with/without 1g/L of NaNO3 for 7 days and various indices of cardiac function and mitochondrial bioenergetics determined. Specifically, the present data demonstrate that NaNO3 supplementation in healthy rats: 1) did not increase in vivo cardiac contractility, 2) did not improve mitochondrial O2 affinity or various indices of cardiac mitochondrial coupling efficiency and oxidative capacity, 3) reduced mitochondrial ADP sensitivity and 4) increased the propensity for mitochondrial reactive oxygen species emission. These data suggest that NaNO3 supplementation does not alter cardiac function in healthy hearts, but is associated with alterations in mitochondria that have been implicated in pathological events. The use of NaNO3 in preventative medicine therefore warrants further investigation in clinical populations.