With Valsalva, Shinzo can make it so that his can increase or slow down the heart rate of whomever he interact with! This quirk can be useful to weaken opponents by making their heart rate so fast that they get tired quickly, or to boost an ally by making their heart rate so that they have increased stamina and energy to fight!
The drawback for this quirk is that it can only be used on one person at a time, and can cause some level of exhaustion on Shinzo.