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2
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the tough membrane surrounding the heart
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3
|
upper chambers of the heart
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4
|
lower chambers of the heart
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6
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another word for pacemaker
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7
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The heart is divided vertically in half by _______.
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8
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largest blood vessels
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|
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1
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The central organ of the ______________ system.
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5
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a muscle responsible for pumping blood to all parts of the body
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