Correct Answer: B

Rationale: The correct answer is B: Atrioventricular Valves. The atrioventricular (AV) valves, including the mitral valve and tricuspid valve, close during ventricular systole to prevent backflow of blood from the ventricles into the atria. They open during ventricular diastole to allow blood flow from the atria into the ventricles. Semilunar valves, choice A, are located at the exits of the ventricles and prevent backflow into the ventricles. The mitral valve and tricuspid valve, choices C and D, are specific types of AV valves.

Correct Answer: A

Rationale: The correct answer is A: Muscle pain. Muscle pain can be a sign of rhabdomyolysis, a serious side effect of statins like atorvastatin. Rhabdomyolysis is a condition where muscle fibers break down rapidly and release their contents into the bloodstream, which can lead to kidney damage. Headache, nausea, and dizziness are not commonly associated with atorvastatin use and are less likely to indicate a serious adverse reaction compared to muscle pain.

Correct Answer: B

Rationale: The correct answer is B: Hypokalemia. Furosemide is a loop diuretic that can lead to potassium loss, resulting in hypokalemia. This electrolyte imbalance is a significant risk associated with diuretic use. Choices A, C, and D are incorrect. Hyperkalemia (choice A) is not typically associated with furosemide use. Hyponatremia (choice C) and hypernatremia (choice D) are related to sodium levels, not potassium levels affected by furosemide.

Correct Answer: A

Rationale: The correct answer is an echocardiogram. An echocardiogram utilizes high-frequency sound waves (ultrasound) to create images of the heart, enabling doctors to evaluate its structure, function, and detect any abnormalities. MRI (Choice B) uses magnetic fields and radio waves to produce detailed images of the body's structures. CT scan (Choice C) combines X-rays and computer technology to create cross-sectional images of the body. X-ray (Choice D) uses electromagnetic radiation to produce images of the internal structures of the body, but it is not the most suitable for assessing the heart's structure and function.

Correct Answer: A

Rationale: The correct answer is A: Contractility. Contractility specifically refers to the change in the force of contraction of the heart muscle without changing its length. In this scenario, the focus is on the change in the inotropic state of the muscle, which directly relates to contractility. Choice B, Excitability, refers to the ability of a cell to respond to a stimulus, not specifically related to changes in contractile force. Choice C, Refractoriness, pertains to the period during which a cell is unresponsive to a new stimulus. Choice D, Automaticity, refers to the ability of cardiac cells to spontaneously generate electrical impulses.