The dye dilution technic is now being extensively used for determination of the cardiac output especially in infants and children. In analyzing the dye dilution curves for the cardiac output, the forward triangle method may be used with reasonable accuracy. The proportionate area of the forward triangle to the entire area of primary circulation varies with different sites of dye injection. The constants of proportionality, used in the forward triangle method, therefore may vary with different sites of dye injection. As more left heart chambers are being explored at the cardiac catheterization study, more specific constants of proportionality are required. Having analysed 102 dye curves inscribed from 15 dogs and 2 children with mild pulmonic stenosis and 1 child with a functional murmur following successive dye injections either into the main pulmonary artery(MPA) or the left atrium(LA),we found that the specific constant of proportionality(K) for the MPA dye curve was 0.27±0.042, and that for the LA dye curve was 0.24±0.042. The cardiac outputs derived from the forward triangle method utilizing the specific K values proposed in this study are reasonably accurate as compared with those by the standard Stewart-Hamilton method. By adopting different K values of 0.27 and 0.24 the estimates from the paired MPA and LA dye curves were found to be very close (r=0.928, p＜0.001), thus the differences caused by different sites of dye injection are corrected.