The purpose of this study is to investigate significance of new method for quantification of left to right cardiac shunts using deconvolution analysis as an adjunct to gamma variate analysis in patients with bad bolus injection. In the present study, quantitative radionuclide angiocardiography (QRAC) was performed with and without deconvolution analysis (DA) in 37 patients with left to right shunt and 103 control patients without shunt. The results obtained were as follows; 1) The mean value of $Q_p/Q_s$ in 103 control patients was $1.10{pm}0.12$ without DA, and was $1.01{pm}0.03$ with DA. 2) Correlation(r) between oximetry and QRAC with DA was 0.87 and correlation(r) between oximetry and QRAC without DA was 0.61. 3) The 13 patients with left to right shunt, whose $Q_p/Q_s$ was greater than 3.0 by QRAC without DA, was studied by DA. Then the $Q_p/Q_s$ values were measurable in these 13 patients by DA and they showed significant correlation with oximetry. (r=0.68) The results indicate that deconvolution analysis technique for quantification of a left to right shunt provides more reliable and accurate shunt quantification, and reduces the influences of poor bolus injection.