Cardiac Cycle Event Sequence

Steps:

• Recall the standard cardiac cycle: atrial systole, ventricular systole, ventricular diastole, atrial diastole.
• Match sequences to physiological order: atria contract first, then ventricles, followed by relaxation phases.
• Eliminate options with reversed or illogical orders, like ventricular events before atrial.
• Confirm the sequence aligning with blood flow: filling, ejection, relaxation.

Why A is correct:

• A follows the defined order of atrial systole → ventricular systole → isovolumetric relaxation → ventricular filling, per cardiac physiology.

Why the others are wrong:

• B reverses systole and diastole, violating contraction-relaxation sequence.
• C places ventricular systole before atrial, disrupting filling phase.
• D omits isovolumetric contraction, incomplete per cycle laws.

Not enough information on exact letter sequences provided.

Final answer: A