A) Thick arrow points to the severely-hypertrophied RV outflow tract that obliterates the infundibular lumen during systole causing dynamic obstruction.
B) Thin arrows point to the level of pulmonary valve leaflets which is at a higher level. This phenomenon leads to desaturation if prostaglandin infusion were discontinued immediately. Prostaglandin infusion should be continued for several days until this phenomenon starts to resolve.