Introduction to physiology; will you help explain this simple paragraph on homeostasis to me ?

Best way to understand is to consider a specific example: the failing heart.  Normally, the heart & kidneys work as a unit, the kidneys monitoring long-term blood pressure, and ensuring adequate blood volume by adjusting retention vs loss of water, and the heart then converts that volume into blood pressure and blood flow.  But when  the heart cannot pump efficiently, and cardiac output falls, that causes a drop in blood pressure.  The kidneys see that drop and act to conserve water, instead of allowing it to be lost. So, the kidney returns more water to the cardiovascular system. BUT, that increased volume can't be converted into cardiac output by the heart, because the heart is not working right. So, by doing what they're supposed to be doing, the kidneys are now making things worse.  All that volume backing up behind a failing heart forces leakage of fluid out of blood vessels, causing edema. As the interstitial space fills up with fluid, the diffusion of oxygen and nutrients decreases, starving cells of what they need.  If its the left side of the heart that's failing, fluid and pressure buildup behind it in the pulmonary system causes difficulty breathing due to fluid leakage into the space around the lungs.  And of course, all that leakage of fluid out of the CV system robs it of volume.  So you can see that it's a vicious cycle that gets progressively worse and worse.  Unless there's an intervention from outside--e.g. a drug like digoxin which improves cardiac contractility--the homeostatic response to the drop in pressure is going to throw the patient further and further off, things get worse and worse.

What part of it don't you understand?