All concepts, explanations, trials, and studies have been
re-written in plain English and may contain errors. I am
not a doctor
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The renin-angiotensin system (RAS) helps regulate the
amount of blood in the body, and blood pressure. The 
RAS is hyper-active in CHF.

Renin is produced by the juxtaglomerular cells of the
kidney. Renin is produced in response to stimulation
from changing amounts of blood in the body and when
blood flow to tissues is reduced - as happens in heart
failure when the weakened heart pumps less blood per
beat.

Angiotensinogen is primarily produced in the liver.
Angiotensinogen is split by renin into angiotensin I.

Angiotensin-converting enzyme (ACE) converts
angiotensin I into angiotensin II.

Angiotensin II binds one of the angiotensin receptors:
AT-1 or AT-2.

Angiotensin II activation of the AT-1 receptor is
more common in the cardiovascular system. This leads
to vasoconstriction, cardiac and arterial wall
enlargement, edema, and increased levels of
vasopressin, endothelin, and aldosterone.

All these substances in turn make CHF and heart
dysfunction worse.

AT-1 receptor blockers (ARBs) specifically block the
RAS by preventing angiotensin II access to AT-1
receptors.