The Valsalva maneuver (“bearing down”) is done by exhaling forcefully with the airway closed, resulting in increased abdominal pressure. While the hemodynamic changes of the Valsalva maneuver are complex and broken into four stages, the main effect occurs during phase 2 which acts to decrease venous return to the heart and blood return to the left ventricle.
The Valsalva maneuver is used during dynamic auscultation to help distinguish different cardiac conditions. The most useful situation is to bring about the murmur of hypertrophic obstructive cardiomyopathy. The murmur of HOCM becomes quite loud with Valsalva. By decreasing left ventricular filling, the left ventricular outflow tract obstruction worsens, making the murmur louder. In patients with aortic valvular stenosis, the murmur will get softer with Valsalva/standing because less blood is being ejected through the aortic valve. Rapid squatting from a standing position forces increased venous return and would have the opposite effect of Valsalva/rapid standing.