All Direct Subsidized and Unsubsidized Loans disbursed between July 1, 2014 and June 30, 2015 carry a fixed interest rate of 4.66% for undergraduates. Graduate or professional students receiving a Direct Unsubsidized Loan disbursed between July 1, 2014 and June 30, 2015 will have a fixed interest rate of 6.21%.
There is a problem when the valve that controls what blood is good and what blood is used, no longer is strong enough to control this flow. Heart valves get damaged or simply wear out. I think you are asking what causes blood to flow in the wrong direction. My guess is that it would be a faulty heart valve.
The valve(s) does not close completely, causing the blood to flow backward through the valve. The heart is forced to pump more blood on the next beat, making it work harder. Stenosis (or narrowing of the valve). The valve(s) opening becomes narrowed, limiting the flow of blood out of the ventricles or atria.