The viscosity of the blood in narrow capillary tubes by Robin Fåhraeus and Torsten Lindqvist (Am J Physiol 96: 562-568, 1931) can be a valuable opportunity for teaching basic hemorheological principles in undergraduate cardiovascular physiology. This classic paper reports that a progressive decline in apparent viscosity occurs when blood flows though glass capillary tubes of diminishing radius, which has later been designated the ‘Fåhraeus-Lindqvist effect’. Subsequent studies have shown that apparent viscosity continues to decline at diameters that correspond to the arteriolar segments of the systemic vascular tree, where the majority of the total peripheral resistance resides and is actively regulated in vivo. Here we present how the paper by Fåhraeus and Lindqvist can be used as a teaching tool and a platform for a plenary discussion of these concepts with undergraduate students, as well as of the relationship between hematocrit, vessel diameter, red blood cell deformability, resistance to blood flow, and how these factors may affect the work of the heart.