Because left ventricular mass may be important in judging feasibility of Fontan type of palliation in tricuspid atresia, this study was undertaken to generate data on left ventricular mass, volume and mass to volume ratio in newborns and infants with tricuspid atresia, native pulmonary stenosis and concordant ventriculoarterial connections prior to any surgical palliation to obtain values for “normal” left ventricular dimensions in tricuspid atresia. The left ventricle was evaluated in the apical two and four chamber view. From these two perpendicular imaging planes, we calculated mass as difference between epicardial and endocardial volume x 1.05 (specific gravity of heart muscle). Mass divided by volume at end-diastole yields the index: mass to volume. Data from 23 newborns and infants with tricuspid atresia were compared to data from 30 age-matched controls with normal hearts. In both patient and control groups, growth of the left ventricle was not linear but related to the 1.4 (volume) or 1.25 (mass) power of body surface area. The equation best describing relation between left ventricular volume and body surface area in normals is volume = 60.7(body surface area)1.4−0.2 ml; in patients with tricuspid atresia volume calculates as 96.7(body surface area)1.4+0.9 ml. In relation to normal infants, infants with tricuspid atresia had a left ventricular volume of 167 (135–206)% of normal and a left ventricular mass of 163 (132–201)% of normal. Left ventricular mass assessed in normals calculates as mass = 59.9(body surface area)1.25+1.3 grams; in patients with tricuspid atresia it calculates as mass= 117.5 (body surface area)1.25−0.9 grams. The index of left ventricular mass to volume in patients with tricuspid atresia measured 1.32, not significantly different from controls, in whom this index calculates as 1.34.