For cardiac gene researches, a method to quantify the cardiac functions is needed. Ventricular pressure-volume loop analysis is a standard tool to evaluate and quantify the myocardial and cardiac functions. The ventricular volume of transgenic mice is typically estimated by using the conductance catheter measurement system, which measures instantaneous ventricular conductance and then converts it into volume. The classic conductance-to-volume conversion equation was proposed by Baan et al. in 1984, but its accuracy is limited. The volume estimation accuracy of Baan's equation versus different possible mouse left ventricular volume ranges is investigated in this work. The results shows that the error of volume estimation is closely related to end-diastolic volume: the error increases with increasing end-diastolic volume. Therefore, it may not be appropriate to use Baan's equation on the mice with the disease of congestive heart failure, which results in larger end-diastolic volumes.