Correct Answer: A

Rationale: The correct answer is Atrial fibrillation. Atrial fibrillation is indeed a type of abnormal heart rhythm characterized by rapid and irregular beating of the atria. This condition can increase the risk of stroke and heart failure. Choice B, Ventricular fibrillation, is incorrect because it refers to a life-threatening arrhythmia that occurs in the ventricles, not the atria. Choice C, Atrial flutter, is incorrect as it describes a different type of atrial arrhythmia characterized by a regular but fast heartbeat. Choice D, Sinus tachycardia, is incorrect because it is a normal increase in heart rate originating from the sinus node, not an abnormal rhythm.

Correct Answer: A

Rationale: Cardiomyopathy is the correct answer. In cardiomyopathy, the heart muscle becomes weak and cannot pump blood effectively, which can lead to heart failure. Myocarditis (choice B) is inflammation of the heart muscle, not specifically causing muscle weakness. Endocarditis (choice C) is an infection of the inner lining of the heart chambers and valves. Pericarditis (choice D) is inflammation of the pericardium, the outer lining of the heart.

Correct Answer: A

Rationale: Cardiac arrest is the correct answer. It is a sudden, unexpected loss of heart function, breathing, and consciousness, typically resulting in death if not treated immediately. Myocardial infarction (choice B) refers to a heart attack caused by a blockage in the coronary arteries. Heart failure (choice C) is a chronic condition where the heart is unable to pump blood efficiently. Atrial fibrillation (choice D) is an irregular and often rapid heart rate that can lead to complications but is not the same as cardiac arrest.

Correct Answer: A

Rationale: The correct answer is A: 'Anorexia can be a side effect of digoxin.' Anorexia, nausea, vomiting, and diarrhea are commonly known side effects of digoxin. Choice B, 'Tachycardia can be a side effect of digoxin,' is incorrect as digoxin is used to treat tachycardia, not cause it. Choice C, 'Constipation can be a side effect of digoxin,' is incorrect as constipation is not a typical side effect of digoxin. Choice D, 'Urinary retention can be a side effect of digoxin,' is also incorrect as urinary retention is not a common side effect associated with digoxin use.

Correct Answer: B

Rationale: The correct answer is B, Aortic valve. The aortic valve is a semilunar valve located between the left ventricle and the aorta. It prevents the backflow of blood from the aorta into the left ventricle. The pulmonary valve (choice A) is located between the right ventricle and the pulmonary artery, not in the Valsalva's sinus area. The tricuspid valve (choice C) is situated between the right atrium and right ventricle, and the mitral valve (choice D) is located between the left atrium and left ventricle, making them incorrect choices for this question.