Identify the correct sequence of the cardiac cycle.
(i) Blood through the pulmonary vein and vena cava enters in left and right atria respectively.
(ii) AVN generates action potential for the ventricles.
(iii) SAN bring about atrial systole .
(iv) Ventricular systole pushes blood away from the heart .

Options

A. `i rarriirarriiirarr iv`
B. `irarriiirarriirarriv`
C. `iiirarr iirarriv`
D. `iiirarrivrarrii rarri`

Answer

To identify the correct sequence of the cardiac cycle, we need to analyze the statements provided in the question step by step.

### Step-by-Step Solution:

1. **Step 1: Blood Entry into Atria**
- Blood enters the heart through the pulmonary vein into the left atrium (oxygenated blood) and through the vena cava into the right atrium (deoxygenated blood).
- **Sequence:** (i) Blood through the pulmonary vein and vena cava enters in left and right atria respectively.

2. **Step 2: Atrial Systole Initiation**
- The sinoatrial node (SAN) located in the right atrium generates an action potential that causes the atria to contract (atrial systole).
- **Sequence:** (iii) SAN brings about atrial systole.

3. **Step 3: Action Potential to Ventricles**
- The electrical impulse from the SAN travels to the atrioventricular node (AVN), which generates an action potential for the ventricles, leading to their contraction.
- **Sequence:** (ii) AVN generates action potential for the ventricles.

4. **Step 4: Ventricular Systole**
- The ventricles contract (ventricular systole), pushing blood away from the heart into the pulmonary artery and aorta.
- **Sequence:** (iv) Ventricular systole pushes blood away from the heart.

### Final Sequence:
The correct sequence of the cardiac cycle is:
1. (i) Blood through the pulmonary vein and vena cava enters in left and right atria respectively.
2. (iii) SAN brings about atrial systole.
3. (ii) AVN generates action potential for the ventricles.
4. (iv) Ventricular systole pushes blood away from the heart.

### Answer:
The correct option is the second one: (i) → (iii) → (ii) → (iv).

---