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Cardiac Cycle Lab
Cardiac cycle- the electrical and mechanical events
that occur in one complete heart beat
Today you will use a physiograph to record the cardiac
cycle in a frog heart and:
▫ Measure and calculate the phases of the cardiac cycle.
▫ Determine the effects of temperature and chemicals on
the heart
▫ Investigate the heart’s absolute refractory period and
heart block
Recording Equipment
• Physiograph – records biological activity
• Myograph – transducer that measures mechanical
force produced by muscle contraction
• Myogram – recording of muscle activity that can
be measured and interpreted
• Stimulator – sends electrical impulses to the
Cardiac Cycle
• Consists of atrial systole/diastole, and
ventricular systole/diastole which creates one
complete heartbeat.
• These phases are controlled by the contraction of
myocardial cells which are stimulated by the
autorhythmic cells.
Frog Heart
Force (g)
Cardiac Cycle
Time (seconds)
Cardiac Cycle
Effects of Temperature on Cardiac Muscle
• Extreme cold- decrease heart rate
• Extreme hot- increase heart rate
Effects of Chemicals on Cardiac Muscle
Chemicals affecting HR are “chronotropic” agents,
while chemicals affecting contractile force are
“inotropic” agents.
▫ Epinephrine- sympathomimetic, increases heart
rate and contractile force.
▫ Acetylcholine- parasympathomimetic, decreases
heart rate
▫ Atropine- parasympatholytic, increases heart rate
Calculating Percent Change
Post treatment – Pre treatment
Pre treatment
X 100
Absolute Refractory Period
• Cardiac muscle tissue has a relatively long
absolute refractory period. This:
▫ Prevents summation and tetany
▫ Ensures filling time for ventricles
Extra Systole
Heart Block
• Heart block - occurs when the ventricles fail to respond to every
depolarization of the SA node or the response is delayed.
• Partial / Incomplete Block
▫ First-degree block: The interval between atrial contraction and
ventricular contraction is prolonged.
▫ Second-degree block: The atrial to ventricular contraction ratio is
altered. The action potentials are not strong enough to pass through to
the ventricles every time. Can be a 2:1; 3:1; or 3:2 ratio of atrial to
ventricular contractions.
• Complete Block
▫ Third-degree block: The conduction between the atria and ventricles
is completely blocked. There will be no correlation between atrial and
ventricular contractions.