The thickest layer of tissue in the heart wall is the:

Correct Answer: C

Rationale: The myocardium, the muscular layer, is the thickest part of the heart wall for pumping.

Correct Answer: C

Rationale: Ectopic beats originate from areas other than the SA node; thus, the SA node itself does not cause ectopic beats.

Correct Answer: A

Rationale: The QRS complex (often referred to as RS in simplified terms) on an ECG represents the depolarization of the ventricles, which initiates ventricular contraction.

Correct Answer: D

Rationale: ACE inhibitor therapy is currently recommended to prevent the development of heart failure in patients who have had a myocardial infarction and as a first-line therapy for patients with chronic heart failure. Digoxin therapy for heart failure is no longer considered a first-line measure, and digoxin is added to the treatment protocol when therapy with other drugs such as ACE-inhibitors, diuretics, and β-adrenergic blockers is insufficient. Calcium channel blockers are not generally used in the treatment of heart failure. The β-adrenergic blockers are not used as initial therapy for new onset heart failure.

Correct Answer: D

Rationale: Bradycardia in athletes results from increased stroke volume and cardiac efficiency, reducing the need for a high resting heart rate.