it's trying to do the same work with the smaller amount of blood as it did with the full amount, ten pints perhaps reduced down to seven, got to keep pump, pump, pump, pump, pump, pump, pump, because that little bit of blood has got to get round and do a lot more work now, okay, so the blood's rushing round and the heart is pushing faster  because it's having to, because it's not enough of the, not so much pressure there, that's why it feels weak, weak and fast, okay?