Questions: Starting with the return of blood to the heart at the top, place the major phases of the cardiac cycle in order. (i) Instructions Ventricular ejection Isovolumetric relaxation Ventricular filling Isovolumetric contraction

The major phases of the cardiac cycle, starting with the return of blood to the heart, are as follows:

1. Ventricular filling: This phase occurs when the ventricles are relaxed, and blood flows from the atria into the ventricles. It includes both passive filling and active filling (atrial contraction).

2. Isovolumetric contraction: This phase begins with the contraction of the ventricles, but the volume of the ventricles does not change because the atrioventricular (AV) valves are closed and the semilunar valves have not yet opened.

3. Ventricular ejection: During this phase, the pressure in the ventricles exceeds the pressure in the arteries, causing the semilunar valves to open and blood to be ejected from the ventricles into the aorta and pulmonary artery.

4. Isovolumetric relaxation: This phase occurs after the ventricles have ejected their blood and the semilunar valves close. The ventricles relax, but the volume does not change because all valves are closed.

In summary, the correct order of the major phases of the cardiac cycle is:

1. Ventricular filling
2. Isovolumetric contraction
3. Ventricular ejection
4. Isovolumetric relaxation