Small resistance artery structure is an independent predictor of cardiovascular events in essential hypertension [1, 2] and diabetes (types I and II) [3, 4]. In particular, the media-to-lumen ratio (M:L) is predictive of cardiovascular events. The exact nature of this resistance artery remodeling is largely unknown, and the presented project aims to investigate this. Innovative multiphoton excitation microscopy will be applied on live (vital), isolated, cannulated and pressurized arteries from parietal pericardial biopsies obtained during open cardiac surgery (coronary artery bypass grafting and cardiac valve replacement surgery). Using the intrinsic properties of the live tissue, that is the autofluorescence of elastin and smooth muscle/endothelial cells and the second harmonic generation from collagen fibers, the quantity, distribution and orientation of elastin structures, collagen fibers, and endothelial and smooth muscle cells will be determined in relation to a range of distending pressures (50, 100, 150, 200 mmHg) and in relation to the frequently determined M:L. We present here our initial results from (pig) pericardial biopsies where we describe the microarchitecture of the tissue in comparison to other well-studied microvascular beds (e.g. rat mesentery). In the future we aim to compare the microarchitecture of small resistance arteries from parietal pericardial biopsies between patients with and without (treated) hypertension, diabetes and/or ischemic heart disease. 1. Buus, N.H., et al., Small artery structure during antihypertensive therapy is an independent predictor of cardiovascular events in essential hypertension. J Hypertens, 2013. 31(4): p. 791-7. 2. Mathiassen, O.N., et al., Small artery structure is an independent predictor of cardiovascular events in essential hypertension. J Hypertens, 2007. 25(5): p. 1021-6. 3. Rizzoni, D. and E. Agabiti Rosei, Small artery remodeling in hypertension and diabetes. Curr Hypertens Rep, 2006. 8(1): p. 90-5. 4. Rizzoni, D., et al., Prognostic significance of small-artery structure in hypertension. Circulation, 2003. 108(18): p. 2230-5.