An X-ray microscopic study of the pattern and distribution of capillary beds in the atria of the human heart

1. The arterial supply to the atria of the human heart was demonstrated by the Coslett Nixon X-Ray Projection Microscope and the small arteriole and capillary beds examined. 2. The “smooth” portion of the wall of the right atrium revealed an irregular pattern of vessels, while the “rough” part showed parallel arterioles in the musculi pectinati, which supplied numerous clusters of capillaries. 3. The wall of the left atrium possessed circumferentially arranged arterioles, which anastomosed with each other and a circular pattern was demonstrated around the orifices of the pulmonary veins. 4. Arterial vasa were demonstrated in the adventitia of the superior and inferior vena cava in their terminal portions, originating from the arterial plexus in the wall of the right atrium. 5. Measurements of capillary densitities showed that this was greatest in the “rough” portion of the right atrium.