A heat exchanger tube having an integral restricting and turbulating structure consisting of dimples formed by confronting indentations pressed into the sides of the heat exchanger tube. The dimples are comprised of indentations disposed in pairs which extend into the tube to such a depth as is necessary to significantly reduce the cross sectional area of the heat exchanger tube and provide a pair of converging, diverging flow nozzles to promote turbulence of the flue gases. The turbulence characteristics of the tube can be controlled by varying the size of the aperture of the nozzles. In certain applications, the dimples are located along the sides of the heat exchanger tube, thereby providing unobstructed drainage for liquids even when the tube is bent into a serpentine shape.