How does valsalva maneuver slow the heart rate down? What's the mechanism?

The valsalva does. not slow the heart rate. It increases the heart rate during the time of increase in intrathoracic pressure due to restricted venous return. Wikipedia has a nice and easy to understand description: https://en.wikipedia.org/wiki/Valsalva_maneuver. If you mean slowing or breaking an episode of SVT it is from compensatory increased vagal tone.

Related Questions

What are some tips to relieve heart palps? I have chronic palps, on diltiazem ER 60mg 2x daily. Still have palps. Valsalva maneuver doesn't help.

Palpitation treat. Treatments include not using caffeine, alcohol , street drugs, smoking and other stimulant substances. Try to learn meditation and other calming techniques, cut out herbal substances, cough and cold medicines, nutritional supplements, see your doctor to be sure no direct heart problem and for treatment if the basics above don't help. Read more...

Can performing the valsalva maneuver while weightlifting exacerbate normal leakage across the valves of the heart if a murmur already exists?

Even not weightlifti. Performing a Valsalva maneuver (of which there are 4 phases) can exacerbate the regurgitation of blood in a number of valve pathologies. If a murmur already exists, the augmentation of blood flow across the valve (or diminution of it) can increase (decrease) the intensity of the murmur. It depends on the valve (mitral? aortic?) & phase of Valsalva. Do you have a concern? Discuss on HealthTap Prime. Read more...
Yes it could. It is a long explanation but you should continue to breath during lifting and avoid grunting and holding breath. Read more...

How dose imipramine incrases heart rate? Whats the mechanism?

Anticholinergic. It has a vagolytic effect i.e., it antagonizes the vagus nerve which would otherwise exert a slowing effect on heart rate so the net effect is for the heart to speed up . Read more...