Apical hyperthyroidism

First heart sound: Occurs at the beginning of the systole, with a low pitch and a long duration (about 0.15 seconds). Causes include vibration caused by contraction of the ventricular muscles, sudden closing of the atrioventricular valve, and subsequent ejection into the aorta. The best auscultation site for the first heart sound is at the fifth intercostal space of the midline of the clavicle or at the right edge of the sternum.