cardiac cycle

1. Compare the duration of systole at resting heart rate (A) and at a rapid heart rate during exercise (B).
- A is greater than B: During exercise, the systole duration shortens to allow for faster heart rates.

2. Compare the volume of blood in the ventricles during isovolumetric contraction (IVC) (A) and during isovolumetric relaxation (IVR) (B).
- A is greater than B: The ventricles have more blood during IVC as contraction has not yet begun.

3. Compare the volume of blood in the left ventricle when the left AV valve opens (A) and when it closes (B).
- A is greater than B: Ventricular filling occurs after the AV valve opens, before it closes.

4. Compare the duration of the refractory period in cardiac muscle (A) and in skeletal muscle (B).
- A is greater than B: Cardiac muscle has a longer refractory period to prevent tetanus.

5. Compare the rate of ventricular filling in early diastole (A) and late diastole (B).
- A is greater than B: Rapid filling occurs initially due to pressure differences.

6. Compare the duration of the refractory period in cardiac muscle (A) to the duration of contraction in cardiac muscle (B).
- B is greater than A: The contraction duration is generally longer than the refractory period.

7. Compare the velocity of impulse through the bundle of His and Purkinje system (A) and through the AV node (B).
- A is greater than B: The Purkinje system conducts impulses more rapidly than the AV node.

8. Compare the rate of depolarization of the SA node on parasympathetic stimulation (A) and sympathetic stimulation (B).
- B is greater than A: Sympathetic stimulation increases the rate of depolarization.

9. Compare the stroke volume when end-diastolic volume equals 130 ml (A) and 160 ml (B).
- B is greater than A: A higher end-diastolic volume typically results in a higher stroke volume.

10. Compare the volume of blood in the left ventricle when the aortic valve opens (A) and closes (B).
- A is greater than B: Blood is ejected during systole, reducing volume by closing.

11. Compare the duration of diastole at resting heart rate (A) and during rapid heart rate during exercise (B).
- A is greater than B: Diastole shortens with increased heart rates.

12. Compare the spontaneous rate of depolarization in the SA node (A) and in the ventricles (B).
- A is greater than B: The SA node has a faster intrinsic depolarization rate.

13. Compare the volume of blood in the ventricles at the onset of IVC (A) and at the end of IVC (B).
- A and B are equal: No volume change occurs during isovolumetric contraction.