Final answer:
Contraction of the upper chambers of the heart is called atrial systole, a phase important for pushing blood into the ventricles, whereas the relaxed state of the atria while ventricles contract is known as atrial diastole.
Step-by-step explanation:
The contraction of the upper chambers of the heart is called atrial systole. During atrial systole, the atria contract, which increases the pressure inside them, thereby pushing blood into the ventricles through the atrioventricular valves. This phase is represented by the P wave on an electrocardiogram (ECG) and is essential for the efficient pumping of blood into the ventricles; this phase contributes to what is known as the "atrial kick" and accounts for the final 20-30 percent of ventricular filling.
In contrast, atrial diastole is a phase where the atria are relaxed and the ventricles contract, which is known as ventricular systole. This sequence of events ensures that blood is ejected from the ventricles and out to the lungs and the rest of the body.