Mechanism behind maneuvers

Respiration:

Murmurs that arise on the right side of the heart become louder during inspiration as this increases venous return and therefore blood flow to the right side of the heart. Left-sided murmurs are either unchanged or become softer. Expiration has the opposite effect
Leaning the patient forwards in full expiration and listening to the base of the heart for aortic regurgitation brings the base of the heart closer to the chest wall

Valsalva:

Decreases preload - increases dynamic outflow tract obstruction, but not fixed
In phase 1 (beginning the manoeuvre), a rise in intrathoracic pressure and a transient increase in left ventricular output and blood pressure occurs.
In phase 2 (the straining phase), systemic venous return falls, filling of the right and then the left side of the heart is reduced, and stroke volume and blood pressure fall while the heart rate increases. As stroke volume and arterial blood pressure fall, most cardiac murmurs become softer; however, because the left ventricular volume is reduced, the systolic murmur of hypertrophic cardiomyopathy becomes louder and the systolic click and murmur of mitral valve prolapse begin earlier.
In phase 3 (the release of the manoeuvre), first right-sided and then left-sided cardiac murmurs become louder briefly before returning to normal. Blood pressure falls further because of pooling of blood in the pulmonary veins.
In phase 4, the blood pressure overshoots as a result of increased sympathetic activity as a response to the previous hypotension. Changes in heart rate are opposite to the blood pressure changes.

Standing to squatting:

This increases venous return, leading to increased preload and stroke volume. This makes most murmurs louder. However, left ventricular size is increased, which reduces the obstruction to outflow and therefore reduces the intensity of the systolic murmur of hypertrophic cardio- myopathy, while the mid-systolic click and murmur of mitral valve prolapse are delayed

Isometric exercise:

Increases arterial resistance and blood pressure leading to increased afterload. The systolic murmur of aortic stenosis may become softer because of a reduction in the pressure difference across the valve but often remains unchanged. Most other murmurs become louder, except the systolic murmur of hypertrophic cardiomyopathy, which is softer, and the mitral valve prolapse murmur, which is delayed because of an increased ventricular volume.