Comparison of mean vessel orientation, vessel alignment and vessel density across hearts. Mean coronary vessel helical angle as a function of depth in the posterior left ventricular wall for n = 4 hearts at (a) embryonic day (ED) 9, and (b) ED13. Depth across the ventricle wall is normalized for all hearts from 0 (closest vessels to epicardium) to 1 (closest vessels to endocardium). A.u. is arbitrary units. Black dashed line indicates the horizontal at 0°. (c) Concentration parameter κ averaged over the first 60% of the tissue starting from the epicardium (left) and the last 40% of the tissue until the endocardium (right) for all hearts at ED9 and ED13. Mean for each group indicated by gray line. (d) Vessel volume fraction (left) and vessel length density (right) for all hearts at ED9 and ED13. Mean for each group indicated by gray line. Groups compared using a two-tailed T-test assuming unequal variance.