A. A S3 heart sound
B. A S4 heart sound
C. A fixed split S2 heart sound
D. A paradoxically split S2 heart sound
E. The early diastolic murmur of mitral stenosis
The S4 heart sound (a.k.a. “atrial gallop), occurs just before S1 when the atria contract to force blood into the left ventricle. If the left ventricle is non-compliant and atrial contraction forces blood through the atrioventricular valves (mitral/tricuspid), a S4 is produced by the blood striking the left ventricle. In atrial fibrillation, atrial contraction is lost and an S4 heart sound is not able to be produced.