A 68-year-old male patient in the cardiology ward complains at each mealtime of difficulty in swallowing (dysphagia). Radiographic studies reveal significant cardiac hypertrophy. A barium swallow, followed by radiographic examination of the thorax, reveals esophageal constriction directly posterior to the heart. Which of the following is the most likely cause of the patient's dysphagia?

Mitral stenosis leads to left atrial dilation, which can exert a compressive effect on the esophagus. The pulmonary valve is located between the outflow tract of the right ventricle and the pulmonary trunk. The aortic valve is located between the left ventricle and the aorta. Anterior interventricular (left anterior descending) and posterior interventricular (posterior descending) arterial occlusions can cause a myocardial infarction, but not dysphagia. In the normal position of the heart the left atrium lies most posteriorly. Therefore, a stenosis of the mitral valve (atrioventricular valve between left atrium and left ventricle) would lead to enlargement of the left atrium, which would in turn impinge upon the esophagus. A stenosis of the pulmonary valve would have no effect upon the esophagus because of the anterior position of the pulmonary trunk in the thorax. Regurgitation through any valve will ultimately decrease systemic blood flow. An occlusion of a coronary artery will lead to ischemia and possibly myocardial infarction.