‘Despite the name, heart failure does not mean the heart has failed completely. Instead, it means the heart isn’t pumping efficiently enough to meet the body’s need for blood.
When the body first detects that it’s not getting an adequate blood supply, it tries to compensate. Stress hormones rise, pushing the heart to beat faster and harder. Blood vessels narrow in an effort to keep blood pressure stable. To keep blood flowing to the heart and brain, the body diverts blood away from less important tissues. The body also retains sodium and fluid in an attempt to supplement the volume of circulating blood.’
For more, please click on source: http://www.health.harvard.edu/healthbeat/what-are-the-symptoms-of-heart-failure