What happens to the heart frecuency during the Valsalva maneuver?

When Pap fainted it was probably because his left vagus nerve was stimulated to a degree that it caused an atrioventricular block, and his heart rate slowed down too much. The drop in blood flow to the brain put him into the Land of Nod. When the vagal stimulation stopped, the block went away, so he normalized his heart rate. About then he had enough time for adrenaline to hit, so his heart rate became higher than his baseline. The right vagus nerve slows the heart by slowing the SA node, and it's unlikely that would have been enough to make him pass out, but it would be enough to slow him down to a point at which the normal compensatory mechanisms would have been blunted, and I'm guessing he has lost enough left ventricular compliance that at a slightly slow heart rate he had the S3. I'd wonder if he has a history of diastolic dysfunction.

You're getting some bad answers!

a doc:  With all due respect, you need to do some reveiew.  Your answer is flatly incorrect relative to both the physical exam points and the physiology of the Frank-Starling curve.

The goal of doing a Valsalva maneuver during cardiac auscultation is 3-fold.  First, it augments the S2 split.  Failure to vary it is called "fixed splitting".  S2 is the sound of the outflow valves closing.  The change in intrathoracic pressure with Valsalva causes pulmonary vascular pressure increase and the pulmonic valve closes early relative to the aortic valve.  Secondly, if a systolic murmur is detected and it decreases with Valsalva, this is suggestive of aortic stenosis because the backpressure in the abdominal and thoracic aorta caused by Valsalva is resisting the turbulent flow.  Last, if a diastolic murmur is detected and it augments with Valsalva, this is suggestive of mitral regurgitation which flows even faster when the heart is being externally compressed by thoracic pressurization.

I don't have to know ANY of that stuff anymore because I just have to detect whether or not the patient has findings suggestive of a potential for operative risk.  At that point, they go for an echo and a cardiology evaluation.  However, I can still tell the difference between mitral regurgitation and aortic stenosis!

Next, the comments about the Frank-Starling mechanism are incorrect.  The Frank-Starling mechanism is a physiologic principle that regards muscle contraction.  When a muscle is stretched a bit, it contracts more efficiently than when it is completely slack.  In the heart, this means that if the chamber is inflated properly, it gets a good mechanical contraction.  If it is under inflated with blood, its contraction is weak.  Also, if the chamber is OVER-inflated, the contraction is weakened.  There is a curved graph that one can generate called the "Frank-Starling curve" for any patient, and it involves how well the heart contracts relative to the amount of blood filling it at the beginning of the cycle.  

The amount of filling at the beginning of the contraction is loosely termed "filling pressure", or "preload".  The Valsalva maneuver actually AUGMENTS preload for a few beats, instead of "decreasing the amount of blood flowing back to the heart" as mentioned above.  If preload is augmented and the heart beats stronger with each stroke, it will tend to slow down.  If the heart is robbed of in-flow like "a doc" suggests, then it speeds up as a reflex.  This rate control mechanism has nothing to do with the Frank-Starling curve which only relates to the concepts of "preload" and "cardiac output".

When the doctor who examined your grandfather mentioned a third sound, it might have been the split S2 sound that comes from forcing the two outflow valves to close at different times.  However, it might also have been a discovered murmur that was too subtle to note without the Valsalva.  There's no way to say from here.  An echocardiogram (ultrasound of the heart) is appropriate at this time.

WWD is basically correct as to how the loss of consciousness took place.  This phenomenon is mediated by the vagus nerve which is part of the autonomic nervous system.  Doing the Valsalva maneuver is often strongly stimulatory to the vagus nerve system at a number of points, including where it interacts with the heart and with the abdominal organs.  "Vagaling down" is a phenomenon of vagus nerve stimulation leading to low heart rate, low cardiac output and transient low blood flow to the brain.  This causes temporary loss of consciousness.  Because the body detects its own blood pressure in a special place along the blood vessels to the brain (the carotid arteries) low blood flow to the brain is almost always followed by a reflexive shift back to high heart rate and high blood pressure caused by a rapid response by the sympathetic nervous system.  

I hope that helps.

I'm sorry you got some confusing information.