The increasing popularity of mitral valve repair and current interest in replacement with a mitral homograft or heterograft warrant a new look at the normal functional anatomy of the system. We conducted a detailed review of the anatomic structure of both the intact and excised mitral apparatus of porcine and human species. The following intact structural dimensions were measured: total annular length, anterior and posterior annular length. Excised measurements included: total annular length, anterior and posterior annular lengths, leaflet edge lengths, leaflet heights, and anterolateral and posteromedial commissural heights. Leaflet area was calculated from planimetric measurements. Chordal lengths were measured and distribution recorded. The majority of leaflet measurements were not statistically different between groups. For both groups, the measured annular length increased significantly upon valve excision. In both groups, the posterior leaflet area was significantly larger than the anterior leaflet area, and the area of each leaflet alone was significantly greater than the calculated orifice area. Chordal length was not significantly different between groups, however, distribution varied slightly with the ratio of origins to insertions being 8:1 (porcine) and 5:1 (human). The results are consistent with previous studies of the human mitral valve. This study showed little difference between human and porcine data, and the porcine valve was identified as an appropriate model for further investigation of the mitral valve system.(ABSTRACT TRUNCATED AT 250 WORDS)