A Blood pressure = stroke volume × heart rate.

[Feedback :- This is the formula for cardiac output. Blood pressure ? blood flow × peripheral resistance.]

B Left-to-right shunting across the duct is normal in the fetus.

[Feedback :- The ductus arteriosus carries relatively more oxygenated blood from the pulmonary artery to the aorta in the fetus, thereby bypassing the lungs.]

C The fetal heart does not start pumping blood until 18–20 weeks, because the placenta performs this function.

[Feedback :- The fetal heart develops in very early fetal life (18 days) and begins pumping blood by day 21. The placenta does not ‘pump’ blood to the fetus.]

D Contractility of the heart is independent of preload and afterload.

This is the Correct Answer

[Feedback :- Unlike stroke volume, contractility is independent of preload and afterload, and is an innate property of myofibrils. It can be influenced by inotropes (e.g. dobutamine).]

E The ductus arteriosus can be kept open by the use of ibuprofen or indomethacin, but these have some side effects.

[Feedback :- These drugs are used to close a patent ductus arteriosus (PDA). Keeping a duct open requires prostaglandin (E₁ or E₂).]