Pericytes are contractile microvascular mural cells, known to have important functions in regulation of the vasculature in health and disease. In the CNS they regulate capillary diameter and initiate an increase in blood flow in response to neuronal activity (Hall et al., 2014). In ischaemia pericytes irreversibly constrict capillaries, contributing to the “no-reflow” phenomenon following stroke. This phenomenon is also observed after myocardial infarction, raising the possibility that myocardial pericytes contribute to ischaemia-evoked constriction at the capillary level (O’Farrell & Attwell, 2014). We investigated the anatomical characteristics of murine ventricular myocardial pericytes to determine the feasibility of a potential role in regulating cardiac capillary diameter and blood flow. Methods: Adult NG2-DsRed mice (n = 5; 3 males, 2 females) were sacrificed using Schedule 1 methods. The hearts were removed and immersion fixed in PFA. Immunohistochemistry was performed on 150 μm transverse sections. Ventricular pericytes were labelled for PDGFRβ and capillaries were labelled with FITC-conjugated isolectin B4. Z-stacks for pericyte quantification were acquired using laser-scanning confocal microscopy and data were analysed using ImageJ software (NIH, Bethesda, MD, USA). Data are presented as mean ± SEM. Results: Pericytes were present in the lateral, septal, and anterior/posterior (not distinguishable in transverse slices) left ventricle (LV) of adult mice at a density of 2.6×107/cm3, 2.5×107/cm3, and 2.5×107/cm3 respectively. The overall LV pericyte density was 2.6×107/cm3. Mouse myocardial pericytes extend NG2- and PDGFRβ-positive processes along and around the surface of coronary capillaries, providing a possible anatomical substrate for control of capillary diameter. In the LV 99.2±0.6% of NG2-DsRed+ pericytes were also labelled by anti-PDGFRβ antibody (2874 pericytes analysed in 36 z-stacks). Moreover, 93.2±0.6% of PDGFRβ+ pericytes were also NG2-DsRed+. Pericytes are as abundant as cardiac myocytes in ventricular tissue. Their high density and anatomical configuration is consistent with them having a role in regulating myocardial blood flow. Use of the NG2-DsRed fluorescent reporter line will enable cardiac physiologists to investigate pericyte physiology and pathology in vivo.