A: Knowing the concepts of preload, after-
load, and cardiac output is critical to under-
standing how the heart functions and how
abnormal function of the heart affects your
patient. This means that you must have a
thorough understanding of these concepts in
order to accurately assess and evaluate your
patient’s cardiac functioning. Medications
are utilized to alter preload, afterload, and
cardiac output to enhance the ability of the
heart to work more efficiently. So you also
need to be able to evaluate the effects of
these medications.
Q: What’s preload?
A: Preload is the degree of stretch in the ven-
tricle at the end of diastole. Hemodynamic
monitoring of central venous pressure (CVP)
at the bedside evaluates right-sided heart
functioning and provides a direct measure-
ment of preload based on volume. Normal
CVP ranges from 0 to 8 mm Hg.
July/August 2008 Nursing made Incredibly Easy! 27
Don’t be puzzled by
cardiovascular concepts
CONNIE GOWDA, RN, MSN
Clinical Assistant Professor • Methodist College of Nursing • Peoria, Ill.
Q: Why are
the concepts
of preload,
afterload, and
cardiac output
so important?
patho puzzler
Understanding preload, contractility,and afterload
If you think of the heart as a balloon, it will help you understand the concepts of preload, contractility,
and afterload.
Preload Contractility Afterload
Blowing up the balloon
Preload is the stretching of mus-
cle fibers in the ventricle. This
stretching results from blood
volume in the ventricles at end
diastole. According to Starling’s
law, the more the heart muscles
stretch during diastole, the more
forcefully they contract during
systole. Think of preload as the
balloon stretching as air is
blown into it: The more air, the
greater the stretch.
The balloon’s stretch
Contractility refers to the inher-
ent ability of the myocardium to
contract normally. Contractility
is influenced by preload. The
greater the stretch, the more
forceful the contraction—or, the
more air in the balloon, the
greater the stretch and the far-
ther the balloon will fly when air
is allowed to expel.
The knot that ties the
balloon
Afterload refers to the pressure
that the ventricular muscles
must generate to overcome the
higher pressure in the aorta to
get the blood out of the heart.
Resistance is the knot on the
end of the balloon, which the
balloon has to work against to
get the air out.
