الفهرس 
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Abstract
This work is an attempt to clarify the effect of different does of caffeine on the frog s heart contractions as well as its effect on the sodium , potassium and calcium contents in both the ventricular muscle and the whole frog s heart.
The results :
1-The enhanced release of calcium from intracellular stores .
2-the inhibitory action of caffeine on phosphodiestrase activity which destroys cyclic AMP thereby , leading to a rapid elevation of cyclic AMP which increases contractile force.
3-Increasing the sensitivity of the contractile protein to calcium