Certain interventions or maneuvers, such as change in patient's body position, can provide important information regarding the significance of a murmur.
Standing → squatting - HOCM
Standing from the squatting position decreases systemic venous return. This momentarily decreases cardiac output and would, for example, decrease the intensity of an innocent murmur. The murmur of hypertrophic obstructive cardiomyopathy (HOCM) on the other hand, becomes louder. Because left ventricular volume decreases, thereby, increasing the degree of obstruction.
Other interventions
Other commonly used maneuvers include the Valsalva maneuver to decrease ventricular filling, handgrip exercise to increase systemic arterial resistance and exercise such as jumping in place to increase cardiac output.
Valsalva maneuver
The Valsalva maneuver is forced expiration against a closed glottis, thereby, increasing intrathoracic pressure, which decreases venous return to both ventricles. The resultant decrease in cardiac output decreases the intensity of all innocent murmurs and most pathologic murmurs. A key point is that a murmur that becomes more prominent with decreased venous return is never an innocent murmur.
Valsalva - HOCM
As an example of using this maneuver, a Valsalva increases the murmur of hypertrophic obstructive cardiomyopathy, while it decreases the murmur of valvular aortic stenosis.