The aim of the study was to determine changes in the blood flow in arterial trunks (coming out of the heart of chickens) by changes of the lumen of these arteries during embryogenesis (on the 10th, 15th, and 19th days) and 6 days after the hatching. For this purpose, posthumous morphometry of aorta, pulmonary arteries, and arterial (Botallo's) ducts (AD) from their exit from the heart until final extraorgan branching was conducted. It was demonstrated that, in this period, (1) initial lumens of aorta and pulmonary arteries are equal to each other and are equally increased (with temporary stop in last quarter of embryogenesis) with an increase of the body weight (BW); (2) the portion of the right ventricle in a total blood circulation minute volume (BCMV) is somewhat smaller than the portion of the left ventricle, but it approaches equality to it by the end of embryogenesis; (3) with the growth of embryos, the portion of total BCMV flowing through the anterior (before the inflow of AD into the aorta) part of the body decreases; that in the average part increases (from 17 to 31%); that in the posterior part (after bifurcation of aorta), where chorioallantoic membrane (CAM) is located, remains almost unchanged; (4) after the hatching (and disappearance of CAM), BCMV of the left ventricle multiply increases due to the junction of two blood flows from the heart (through the ascending aorta and AD) into a single flow, which flows sequentially by lesser and greater circulations, resulting in multiple increase in the organ blood flow.