"Parasternal heave (lift) occurs during right ventricular hypertrophy (i.e. enlargement) or very rarely severe left atrial enlargement." RV hypertrophy can be seen so easily because the RV is at the anterior surface of the chest.
In this patient blood from LA to LV decreases in saturation, so it is going somehwere. From the O2 sat. we can deduce there is probably a VSD (increased RV pressure would cause RVH and parasternal heave). Furthermor, the vignette is likely describing tetralogy of fallot (caused by anterosuperior displacement of the infundibular septum). In Tet spells, RV outflow is too obstructed and patient gets cyanosis and R>L shunting Squats increase SVR, decreasing R>L shunting, putting more blood through pulmonary circuit and relieving cyanosis.
Notice drop of O2 saturation from LA (95%) to LV (70%) & equal O2 saturation between LV (70%) & RV (70%) --> VSD is present
Notice the pressure of the RV (120/6) – Normal RV pressure is 25/5 which indicates increased pressure because of the increased volume of blood coming from the LV through the VSD
Grade 4 murmur is a palpable thrill most likely due to RVH from the overloaded work
I just want to mention that kids squatting is very much suggesting a TOF in USMLE..lol. And her pulmonary murmur suggests pulmonary stenosis, which further supports TOF.