The first heart sound is usually the beginning of the systolic phase of the heart, lasts longer, and has a lower tone than the second heart sound. It is produced mainly by the sudden closure of the mitral and tricuspid valves, including the contraction of the ventricles, and the subsequent opening of the mitral and tricuspid valves, and by the vibrations caused by the blood ejected from the ventricles and right ventricle into the aorta and pulmonary artery. The first heart sound can be clearly heard at the site of auscultation, usually at the 5th intercostal space at the left border of the sternum, or at the 3rd intercostal space at the left border of the sternum. First heart sound augmentation can occur in conditions such as altered anatomic nature of atrial accompaniment and diastolic filling of the ventricles. In addition, diminished first heart sounds can be due to mitral and tricuspid valve closure insufficiency and more regurgitated blood.