Individual microvascular units are critical to cardiac performance

High cardiac energy demand relies on lipid & glucose oxidation, depending on oxygen availability. Arteriolar supply is likely critical with loss of metabolic flexibility/rarefaction of capillary supply, e.g. diabetes or hypertension. Random blockade of coronary arterioles by infusion of microspheres decreased rate‐pressure product (RPP; R2=0.82) and peak developed pressure (P<0.01). This decreased RPP by 70% (P<0.001) in control & diabetic perfused‐working hearts. Palmitate oxidation halved (P<0.001) with a similar increase in glucose oxidation (P<0.01) for control hearts, but in diabetic hearts palmitate oxidation was 2.5‐fold higher (P<0.001) with unchanged glucose oxidation (ns). Arteriole occlusion decreased the density of patent capillaries by 40% (P<0.001) and increased capillary supply area by 60% (P<0.01). There was a more heterogeneous distribution of functional capillaries in the myocardium following microsphere infusion (CV=19.15% untreated vs. 25.80% occluded). We suggest that capillary supply is more critical for cardiac mechanical performance than preservation of metabolic flexibility, and supports the importance of preventing arteriole loss as a consequence of microvascular disease.