The aim of this work was to address morphometric patterns of coronary artery (c.a.) development in the rat based on serial section analysis of hearts at different stages of prenatal development. Studies were performed on foetal hearts 15-21 days (ED) post-conception. Paraffin sections were stained with haematoxylin-eosin (H & E) and frozen sections were labelled with Griffonia simplicifolia I (GSI) lectin (endothelial cell marker). Coronary arteries™ luminal diameters were measured at different distances from the aortic roots and the main c.a. branch lengths were calculated from serial sections. All measured values were compared to heart length and to foetal stages. On ED15 precursors of c.a. were distinguished as tubes running on both sides of the outflow tract. Below the aortic valves the tubes had the largest diameter. Formation and development of c.a. proceeded by elongation of vascular tubes distally, ramification and formation of the media and the adventitia. During the prenatal period the c.a. length increased approximately 14-fold, while heart length increased about 4-fold, and crown-rump length about 2.5-fold. The lumen of the proximal part of c.a. increased 4-fold during ED18±21. An increase in c.a. length is the fastest compared to the heart growth, and crown-rump growth during the foetal life
