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The hearts 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). Results showed 9 young animals (2-3 years old), with 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 as compared with 3 older llamas (aged 5-7 years old). This results in an increase of the 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 µm2 resp. 17.5 µm; right ventricular wall,156 µm2 resp. 15.5 µm; left auricle, 96 µm2 resp. 11.5 µm). It is suggested that the morphological conditions of the cardiac vascular supply of llamas living at an altitude of 4000 m improve with age.