Background/Objectives A considerable number of patients with symptoms of chest pain during exercise have no functional relevant stenosis in their coronary arteries. In these patients the angina may relate to coronary microvascular dysfunction as a consequence of glycocalyx loss; since the latter has been associated with an impaired ability of adenosine to increase microvascular blood volume, we hypothesize that non-invasive measurements of myocardial microvascular blood volume recruitment with MRI could diagnose patients with coronary glycocalyx loss. As a first step, we measured in the current study coronary microvascular blood volume using first-pass dynamic contrast-enhanced MRI to assess myocardial microvascular blood volume in healthy control rats under baseline conditions and during adenosine infusion. Methods Rats (male, 300-450g, n=5) were anaesthetised with isoflurane (induction chamber 4,5% isoflurane and 1% oxygen, during experiment 2% isoflurane and 0,4% oxygen). MRI was performed on a 7.0 Tesla Bruker Biospec animal scanner. A bolus of 150 µl Gadovist (Gd-DTPA) was injected in the femoral vein, while scanning continued. The method was optimized to capture the first pass of the contrast agent through the heart. Measurements were performed at baseline and during intravenous adenosine infusion (3 mg/ml; 1,5 ml/h). In the first-pass perfusion images, regions of interest (ROI) were placed in the left ventricular (LV) lumen and in the myocardium of the LV wall. Signal intensity-time curves were calculated for all ROIs and were corrected for baseline. The following semi-quantitative parameters of myocardial perfusion and volume were derived from these curves: total area under the curve (AUC), peak intensity and the upslope to the peak. Results Values are percentages of changes after adenosine infusion compared to baseline ± S.E.M., compared by t-test. A significant increase of 47% ± 14 in total AUC was seen in rats after intravenous adenosine infusion compared to baseline (P<0.05). Peak intensity increased significantly with 49% ± 36 in rat hearts during adenosine infusion compared to baseline conditions. Also a significant increase (63% ± 64) was seen for the upslope of the first-pass peak during adenosine infusion compared to baseline conditions. Conclusion Adenosine-induced increases in myocardial microvascular blood volume in the rat heart are reflected by increases in first-pass MRI-derived contrast intensity. Our next step is to study the effect of glycocalyx damage on myocardial microvascular blood volume recruitment in rats using pharmacological and dietary degradation of the glycocalyx.