A 4-year-old girl with tetralogy of Fallot (TOF) is brought to the pediatric clinic for preoperative evaluation before surgical repair. Her mother reports that the child squats frequently during play and becomes less breathless after squatting. Echocardiography shows a large ventricular septal defect (VSD), overriding aorta (60% override), right ventricular hypertrophy, and pulmonary stenosis. Which of the following best explains the physiological benefit of the squatting posture in this child?