S4 - Fourth Heart Sound

S4	Atrial Gallop (presystolic)
cardiac cycle	Tele-diastolic. produced by a strong left atrial contraction in Patients with decreased left ventricular compliance.
character	Low-pitched, dull sound.
Auscultation	Bell. S4-S1---S2 'daLUB dup' Left S4 = apex, expiration, left lateral decubitus. Accompanied by palpable presystolic impulse of the left ventricle (MI, systemic HTN, HCM, anemia, thyrotoxicosis).
Comments	Normal in young people. Indicates ventricular decompensation. Worst prognosis than S4.