s3 is heard in MR(Mitral regurgitation) it is a diastolic sound,low pitched sound and pathological in adults The third hea sound (S3), also known as the "ventricular gallop," occurs just after S2 when the mitral valve opens, allowing passive filling of the left ventricle.CLINICAL PEARL: A S3 hea sound is often a sign of systolic hea failure, however it may sometimes be a normal finding. Ref Harrison 20th edition pg 1435