BACKGROUND: Knowledge of heart valve vascularity is an important factor for understanding the valvular pathology and to develop tissue-engineered valves for repair procedures. Some investigators believe that blood vessels may exist in normal human heart valves whereas some recent publications have proposed that the presence of blood vessels in the valves is secondary to inflammation. METHODS: Tissues from 60 normal formalin-fixed human hearts were examined microscopically for type, location, and number of vessels in atrioventricular valves. The age of the patient ranged from 10 to 70 years, and an attempt was made to study the age-related morphologic changes in atrioventricular valves. RESULTS: Of the 60 tricuspid and 60 mitral valves examined, 12 tricuspid (20%) and 14 mitral (23.33%) valves were found to have vessels without the presence of an inflammatory process. In tricuspid valves the vessels were observed mainly in the fibrosa layer with a range of 1 to 4 vessels, whereas in mitral valves the vessels were situated mainly in the spongiosa layer with a range of 1 to 2 vessels. The maximum vascularity was seen in the fourth decade of life, in which the vessels were found in 40% of both tricuspid and mitral valves. The mean transverse diameter of these vessels was 0.23 ± 0.18 mm, with a range of 0.06 to 0.79 mm in tricuspid valves, whereas it was 0.15 ± 0.08 mm, with a range of 0.04 to 0.4 mm in mitral valves. The capillaries (3-11 capillaries) were found scattered in the fibrosa and spongiosa with an average lumen area of 0.39 ± 0.18 mm(2). CONCLUSIONS: The blood vessels in atrioventricular valves also can be seen in the absence of inflammation and are likely to be a necessary component of valve leaflets. Thus, when performing procedures involving in situ tissue engineering and valve repair the physician needs to be aware of the presence of these vessels in human heart valves.