The human heart pumps oxygen to the body, and the heart itself requires oxygen.
Both the body and the heart use energy, usually expressed in calories or ergs.
If we look at the energy consumption (in Watts) of the heart as a fraction $F$ of the energy consumption of the body as a whole it is about
$F \approx \frac{1.3}{91.3}=0.014.$
Humans consume about 550L of oxygen per day per this website and the heart itself consumes about 8 ml of $O_2$ per 100g per minute at rest according to this site. Assuming an average global human heart mass of about 310g (Google) the daily total heart oxygen consumption is about (8ml x 3.1 x 1440 min) = 35712 ml or 35.7L of oxygen. The ratio $R$ of heart to body oxygen consumption is thus about
$R \approx \frac{36}{550-36} = \frac{36}{514} =0.07$
These figures are rough at best but not rough enough to account for a discrepancy of a factor of 5 in the ratios. Can someone suggest what might account for the difference?
The calculation seems to show that the heart's proportional consumption of oxygen is a lot higher than its proportional consumption of energy. My understanding is that the respective oxygen consumption of the heart and body are a good reflections of their respective energy consumption. Is that a sound assumption?
Thanks for any insights.