The

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complex represents the depolarization of the ventricles, which requires a much stronger electrical signal due to the larger size of the ventricular cardiac muscles.

A. The volume of blood remaining in the ventricle after ventricular systole: This refers to the end-systolic volume (ESV), which is the amount of blood left in the ventricle after contraction. While ESV is a component used to calculate stroke volume, it does not itself represent the volume of blood ejected with each heartbeat.

B. The pressure exerted by the left ventricle to open the aortic valve: The pressure generated by the left ventricle during systole is termed ventricular systolic pressure. Although this pressure must overcome aortic pressure to allow ejection, it is a measure of force, not volume, and therefore does not define stroke volume.

C. The difference between end-diastolic volume (EDV) and end-systolic volume (ESV): Stroke volume represents the actual volume of blood ejected from the ventricle with each heartbeat. It is calculated as SV = EDV – ESV. EDV is the total ventricular volume at the end of filling, and ESV is the residual volume after contraction. This difference reflects effective cardiac output per beat.

D. The total volume of blood in the ventricle before contraction: The total volume of blood prior to contraction is the end-diastolic volume (EDV). While EDV contributes to determining stroke volume, it alone does not represent the volume of blood expelled during systole.

A. P: The P wave represents atrial depolarization. It reflects the electrical activity as the impulse spreads from the sinoatrial (SA) node across the atrial myocardium, causing atrial contraction. Because the atria are smaller than the ventricles, the electrical signal is smaller in amplitude.

B. QRS: The QRS complex represents ventricular depolarization. It corresponds to the rapid spread of electrical impulses through the ventricles via the bundle branches and Purkinje fibers, leading to ventricular contraction. Since the ventricles have significantly greater muscle mass than the atria, this depolarization produces a larger and stronger electrical signal on the ECG.

C. T: The T wave represents ventricular repolarization, the process by which ventricular muscle cells return to their resting membrane potential after contraction. It does not represent depolarization.

D. PR: The PR interval reflects the time required for the electrical impulse to travel from the atria through the atrioventricular (AV) node to the ventricles. It represents conduction delay, not ventricular depolarization itself.