Final answer:
The additional blood volume added to the ventricles from atrial contraction is called the 'atrial kick', occurring during atrial systole and contributing to the final 20-30% of ventricular filling.
Step-by-step explanation:
The contribution of blood that is added to the ventricles as a result of atrial contraction is known as the atrial kick. During the cardiac cycle, after the atria have filled the ventricles with about 70-80% of their blood volume passively during diastole, the atria contract and provide the remaining 20-30%, thereby completing ventricular filling. This atrial contraction phase is referred to as atrial systole, and the additional volume of blood it pumps into the ventricles is crucial for optimizing the efficiency of the heart's function.
The process begins with the atria contracting following an electrical impulse that is indicated by the P wave on an Electrocardiogram (ECG). Blood is pushed through the open atrioventricular (tricuspid and mitral or bicuspid) valves into the ventricles, and after approximately 100 ms of this activity, the atria return to a relaxed state, or diastole, just before the ventricles begin their own contraction phase called ventricular systole. It's the coordinated action of these phases that allows the heart to pump blood effectively throughout the body.