9. Which of the following alterations of heart sounds would likely be heard in a patient presenting with unstable angina or a non-ST elevation myocardial infarction active myocardial ischemia?

A. Fixed split S2 heart sound

B. The presence of an S3 heart sound

C. The presence of an S4 heart sound

D. Decreased intensity of the S1 heart sound

An S4 heart sound may be present during myocardial ischemia due to the lack of ATP production impairing left ventricular relaxation. Recall that myocardial relaxation is an active process requiring ATP which is reduced during ischemia and a S4 heart sound occurs when a non-compliant, stiffened left ventricle receives blood after atrial contraction.

The fourth heart sound, also known as the "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 AV valves (mitral and tricuspid), an S4 is produced by the blood striking the left ventricle.