Which heart sound may be heard on auscultation that suggests heart failure in the setting of MI?

• A. S4
• B. Murmur
• C. S3
• D. None

Answer: (C)

An S3 heart sound signals volume overload and reduced left ventricular function. In a myocardial infarction, the LV often becomes weak and dilates, so blood rapidly fills the ventricle during early diastole after S2. This rapid filling creates a low-pitched gallop heard best with the bell at the apex in the left lateral position. The presence of S3 indicates elevated filling pressures and congestive heart failure, which commonly complicates an MI with LV dysfunction.

By contrast, an S4 reflects a stiff ventricle from long-standing hypertrophy or diastolic dysfunction, not the acute failure process you’d expect after an MI. A murmur could point to a structural valve issue (like mitral regurgitation from papillary muscle dysfunction) but isn’t the general sign of heart failure in this setting. So the S3 gallop is the best clue that heart failure is present after an MI.