Infective endocarditis is diagnosed using the Duke criteria, which split findings into major and minor categories. Major criteria reflect strong evidence of infection of the endocardial surface: a typical organism in blood cultures (often in more than one culture) or positive cultures persistently, and imaging evidence of endocardial involvement such as vegetation seen on echocardiography or new-valve regurgitation. Fever, while common in many illnesses, is nonspecific and is classified as a minor criterion because it doesn’t by itself prove endocardial infection. Thus, fever ≥38.0°C is not a major Duke criterion. The other findings—positive blood cultures, vegetation on echocardiography, and new valvular regurgitation—are all major criteria.

Understanding prevalence helps here: ventricular septal defect is the most common congenital heart defect. It is a hole in the wall between the heart’s lower chambers, which allows a left-to-right shunt. Many small VSDs close on their own as the child grows, while larger ones can cause symptoms from heart failure and pulmonary overcirculation if not addressed. Atrial septal defects are relatively common too, but not as frequent as VSDs. Patent ductus arteriosus is especially common in premature infants, yet it does not exceed VSD in overall frequency. Tetralogy of Fallot is much less common than VSD. That’s why this defect is the best answer.

The main idea is identifying the most common underlying disease that progresses to congestive heart failure. Coronary artery disease is the leading cause, because ischemic damage from CAD often leads to myocardial scar and systolic dysfunction (ischemic cardiomyopathy), which reduces the heart’s pumping ability and drives heart failure. Hypertension plays a huge role as a risk factor and often leads to heart failure over time, especially causing diastolic dysfunction, but when asked for the single most common cause, CAD typically leads the list. Valvular disease and arrhythmias can cause heart failure too, but they are less commonly the primary etiology compared with CAD.

The main concept is that blocking beta-adrenergic receptors can worsen asthma. In the lungs, beta-2 receptors normally cause bronchodilation when stimulated. A beta-blocker that blocks both beta-1 and beta-2 receptors (nonselective) removes this bronchodilatory influence, making bronchial smooth muscle more prone to constrict and triggering or worsening asthma symptoms. Because of that, beta blockers are avoided in asthma patients. If a beta blocker is absolutely necessary, a cardioselective agent that primarily blocks beta-1 receptors (with little effect on beta-2) can be considered at the lowest effective dose, but still with caution and close monitoring for bronchospasm. In contrast, the other classes listed do not inherently provoke bronchoconstriction: ACE inhibitors can cause cough due to irritation but not bronchospasm; calcium channel blockers and diuretics do not directly impair bronchial dilation and are generally usable depending on the clinical scenario.