Our purpose in this study was to investigate the perivasculary space under the myocardial bridges (MB) in dog, sheep, goat and human hearts. A total of 160 hearts were studied, and perivasculary space under the myocardial bridges was examined under microscope. The specimens belonged to 25 dogs, 100 sheep, 25 goats and 10 humans. Special attention was paid to evaluate the distance between the MB and coronary arteries (CA), CA and underlying myocardium (UM) and to find the relation of concomitant vein number accompanying the CA and MB. 219 myocardial bridges were found in total of hearts, and specimens from these bridges were examined under microscope. There were large variations in distance between the MB and CA (0-714 mum) and distance between CA and UM (0-309 mum). The myocardial bridges were classified into three groups in terms of the number of veins accompanying CA, the bridges with no concomitant veins with one concomitant vein and with two concomitant veins. This suggests that the distance between the MB and CA is crucial to determine how much force is on the CA. The environment surrounding the CA may be a crucial factor in determining whether the MB influences the induction of heart disorders or not.