Myocardial functions can be characterized from ventricular pressure-volume relations. In small animals, the instantaneous ventricular volume is typically measured by using a miniaturized conductance catheter. In this work, a DSP-based conductance catheter measurement system is proposed, which adopts the admittance measurement method to estimate the myocardial contribution, and Wei’s nonlinear equation to convert the blood conductance to volume. In vivo rat experiments were performed with the proposed measurement system, and real-time left ventricular pressure-volume relations can be obtained.