Cardiac shunt calculations made easy: A case-based approach

On the basis of an interesting case of a 40-year-old lady with an atrial septal defect, we describe a simple approach for complex shunt volume calculations based on the Fick principle using hemodynamic data obtained in the catheterization laboratory. Understanding Fick's principle allows determination of all relevant flows, flow ratio, and resistances without having to resort to memorization of complex formulae. Those findings significantly impact the managements of patients like ours with hemodynamically and clinically relevant shunting.