The heart of 12 adult llamas, one female and 11 males, 2-7 years of age, was studied gross-anatomically (absolute and relative heart weight) and microscopic-anatomically (left and right ventricular wall, left auricle). Comparing the 9 younger animals (2-3 years old) with the 3 older llamas (5-7 years old) a significant increase of the absolute heart weight and of the number of capillaries per mm2 and a significant decrease of the intercapillary distance in the left ventricular wall was found. This results in an increase of capillarity in the studied heart regions (5.5% compared to 6.9%). The simultaneous increase of the capillary-to-myocyte-ratios from 0.9 to 1.1 shows a significant correlation to the cross-sectional area of the myocytes (r = 0.79) and an also significant but negative correlation to the number of myocytes per mm2 (r = -0.82). In both groups the cross-sectional area of the myocytes and their diameter differs significantly in the three regions of the heart (left ventricular wall--214 micron 2 resp. 17.5 microns; right ventricular wall--156 micron 2 resp. 15.5 microns; left auricle--96 micron 2 resp. 11.5 microns). It is to be supposed, that the morphological conditions of the cardiac vascular supply of llamas living in an altitude of 4000 m are improving with age.