When relaxed, the atria expand, and then the ventricles contract.
Yes, atria contracts before the ventricles.
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bubble up and popno one knowsthe signal causes the atria to contract.
tricuspid valve
the atriventriculart node causes both atria to contract
Blood flows into the relaxed atria while the ventricles contract. <rephrased> The ventricles contract, carrying blood into the aorta, and blood flows into the relaxed atria.
The atria.
The blood is squeezed into the ventricles.
semilunar valves
Premature Ventricular Contractions
Nodal or pacemaker cells.