What comprises the cardiac cycle?

What comprises the cardiac cycle?

• A. The sequence of atrial and ventricular systole and diastole.
• B. The electrical impulses only.
• C. The mechanical phase of ventricles only.
• D. Blood flow through arteries.

Answer: (A)

The cardiac cycle is the full sequence of mechanical events that make one heartbeat, including the contraction and relaxation phases of both atria and ventricles. The best description is the progression through atrial systole, then ventricular systole, followed by atrial and ventricular diastole. At the start, the atria contract (atrial systole) to top off the ventricles with blood. Next, the ventricles contract (ventricular systole) to eject blood into the pulmonary artery and the aorta. Then both chambers relax (diastole), allowing the ventricles to fill again while the atria fill and then optionally contract a bit more to complete ventricular filling—the so-called atrial kick. The cycle is coordinated by electrical activity, but the defining aspect is the actual mechanical sequence of atrial and ventricular contraction and relaxation. Choices focusing only on electrical impulses miss the mechanical sequence, and describing only the ventricles or only blood flow through arteries leaves out the full, coordinated pattern that constitutes a heartbeat.

The cardiac cycle is the full sequence of mechanical events that make one heartbeat, including the contraction and relaxation phases of both atria and ventricles. The best description is the progression through atrial systole, then ventricular systole, followed by atrial and ventricular diastole. At the start, the atria contract (atrial systole) to top off the ventricles with blood. Next, the ventricles contract (ventricular systole) to eject blood into the pulmonary artery and the aorta. Then both chambers relax (diastole), allowing the ventricles to fill again while the atria fill and then optionally contract a bit more to complete ventricular filling—the so-called atrial kick. The cycle is coordinated by electrical activity, but the defining aspect is the actual mechanical sequence of atrial and ventricular contraction and relaxation.

Choices focusing only on electrical impulses miss the mechanical sequence, and describing only the ventricles or only blood flow through arteries leaves out the full, coordinated pattern that constitutes a heartbeat.