"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.