A morphometric study of foetal and newborn cardiac growth in the horse.

A morphometric study of hearts in 81 equine foetuses, ranging in age from 190 to 330 days of foetal age, and in 26 newborn foals is reported. The mean weight, external dimensions, ventricular wall thickness and circumference of the atrio-ventricular orifice were measured. Features of the main associated vessels of the heart were also recorded. All cardiac measurements of foetuses increased linearly throughout the latter half of pregnancy and were highly correlated with foetal age. This linear growth pattern was also found in the parameters of the associated arterial trunks. The ratio of the right ventricular weight to the total ventricular weight in the equine foetuses increased gradually from 0.27 (Day 190) to 0.34 (full term), but in newborn foals, this ratio began to decrease soon after birth, declining from 0.32 to 0.28 by 11 days of age. The interventricular septum was thickest followed by the right ventricular wall, and the left ventricular wall was thinnest during the period of gestation studied. The right ventricle was 3.2 per cent to 31.5 per cent thicker than the left ventricle.