Discussion on calculation of intracardiac shunts by cardiac cath and Flamm formula.
Pulmonary blood flow is designated as QP and systemic blood flow as QS in hemodynamic calculations. When there is a left to right shunt, pulmonary blood flow is more than the systemic blood flow. The systemic blood flow is more than the pulmonary blood flow when there is a right to left shunt. Calculation of shunt ratio is useful in deciding the operability of shunt lesions as well as their hemodynamic significance.