Meager quantitative anatomic information is available regarding the orientation of the left ventricular outflow tract (LVOT) relative to the ventricular septum (VS), or the relation of these variables to patient age, sex, or other cardiac features. We studied 57 formaldehyde-fixed adult human heart specimens at autopsy from 29 men and 28 women ranging in age from 20 to 91 years (mean age = 66 years). Blinded measurement of 10 morphologic parameters, repeated on 2 occasions, included anatomic indexes of VS sigmoidity (angle between the aortic and the mitral plane). While sigmoidity was not correlated with patient height, body weight, body mass index, cardiac mass (or presence of systemic hypertension), cause of death, or VS length, it was significantly (p less than 0.05) progressive through age groups 20-39 years, 40-59, 60-79 and greater than or equal to 80. The overall correlation of aortic-mitral plane angle (A-MPA) with age was +0.59 (P less than 0.0001), a relationship also noted within each age group. The mean A-MPA increased from 118 degrees to 127, 131 and 134 considering all specimens. Men had consistently greater sigmoidity than women. The steady increase in sigmoidity of the ventricular septum from early adulthood may alter clinical conclusions about pathologic conditions which are based on septal curvature or prominence.