A thorough knowledge of statistical properties of the coronary artery tree is very important in cardiology. We present generalised form of Murray’s law—the first law that described the relationship between vessel diameters in bifurcation. We show that other frequently used laws: Huo-Kassab and Finet’s rules are the special cases of its generalised form. We show theoretically that the Finet’s law is met with an apparently paradoxical relationship between the lengths and diameters of the vessels. Based on the analysis of CT 3D scans, we show that in the left coronary artery the diameters and lengths of vessels are inversely proportional which explains the applicability of the Finet’s law. We justify theoretically the value of coefficient defining Finet’s law.