Mr. F might be having a fluid imbalance/excess .
When you take out a lot of fluid you should be put a lot too, unless you are dehydrated.
But if you are dehydrated, increasing fluid intake will lessen your heart rate not increase it. So it more likely to be a problem with heart or kidney. When your kidney has a disease and body can't remove excess water, the heart workload will increase and it can cause a reduction in blood pressure or increased heart rate.
