General
Sounds generated by rapid ventricular filling are often called “gallop rhythms” or third/fourth heart sound; S3 and S4.

Both sounds are of low frequency, S3 occurring in early diastole, S4 in late diastole.

S3 is the result of blood hitting the opposite left ventricular wall when the mitral valve opens.

S4 is occurring in the second period of rapid diastolic filling; during atrial contraction. It is the result of extra forceful atrial contraction caused by stiffening of the ventricle.

S3 can occur in healthy children and young adults and is then not considered pathological. In patients above the age of 40 the presence of S3 is recognized as an early indicator of heart disease.

S4 is not a common finding in the young and healthy and is considered a sign of heart disease.