Age-induced remodeling of the coronary resistance artery network is an important component of deteriorated heart performance in the elderly. We still do not have a detailed knowledge of this process. Networks of the left anterior descendent coronary artery of young (3 month) and old (appr. 18 month) were compared. We intended to identify the processes induced by advanced age. The whole resistance artery network (down to 80 mm diameter) was microsurgically prepared, left in situ, and video-microscopically examined while perfused through the orifice. The picture of the network was analyzed in a coordinate system determined by the orifice-apex axis. As a sum, 266 vascular segments, 125 branchings and formed from them 9797 50 mm long vascular ring units from 8 young and 7 old male rats were analyzed for their diameter, direction of axis and location in the coordinate system. To identify the processes of segmental and network remodeling, ring unit frequency was plotted against diameter and distance (directly or following the route of flow) from the orifice. Aged animals had heavier hearts with larger orificium-apex distances (2.06±0.24 vs. 1.27±0.06 gr; 17132±1404 vs. 14419±941 mm, p<0.05). A newly formed wider population (> 600 mm) appeared in the older hearts as a result of elongation and morphological distension of 400 mm vessels. A population peak of 200 mm vessels moved up to 300 mm, resulting rarefaction in the population of smaller vessels. Two clusters formed a substantial part of ring population in the youngsters: 300-450 mm diameter vessels located 3–8 mm from the orifice and 150–350 mm vessels in a distance of 7–13 mm from the orifice. However, there was a disintegration of these clusters in the elderly. In old networks the tortuosity of 300 mm vessels increased (p<0.03) and also increased the deviance of ring unit axes from the orifice-apex angle (p<0.01). Thus, more distance should be covered by the flow to travel the same direct distance from the orifice (p<0.01). On the other hand, diameters of daughter branches in both young and old networks well complied with the Murray's law. Axial elongation, radial distension, axial and radial displacement acting in concert and separately form the basic processes of age-induced remodeling of the rat coronary resistance artery network. As a result, a network with a more zigzagging route will be produced, which seems to be hemodynamically less advantageous. (Supported by OTKA TO 32019 and 42670, the Hungarian Hypertension Society and the Hungarian Kidney Foundation).