Cardiac Cycle Event Sequence

Steps:

• Recall the cardiac cycle phases: atrial systole, ventricular systole (isovolumetric contraction and ejection), ventricular diastole (isovolumetric relaxation and filling).
• Match sequences to standard order: atria contract first, then ventricles, followed by relaxation and refilling.
• Eliminate options that reverse systole/diastole or misplace atrial/ventricular events.
• Identify the option aligning with physiological flow from ECG waves (P, QRS, T) to mechanical events.

Why C is correct:

• C follows the defined order: atrial systole → ventricular systole → ventricular diastole → atrial diastole, matching the cycle's pressure-volume loop.

Why the others are wrong:

• A: Starts with ventricular systole before atrial, violating initiation by atrial contraction.
• B: Places diastole before systole, inverting contraction-relaxation sequence.
• D: Ends with atrial systole after ventricular events, disrupting refilling timing.

Not enough information on exact letter sequences for choices.

Final answer: C