This patient's presentation with exertional dyspnea, pounding heart sensation, and widened pulse pressure is most likely due to chronic aortic regurgitation (AR).  In chronic AR, a portion of left ventricular (LV) output leaks back into the left ventricle, causing an increase in LV end-diastolic volume (LVEDV), myocardial hypertrophy, and chamber enlargement.  The increase in LV size brings the ventricular apex close to the chest wall, causing a pounding sensation and an uncomfortable awareness of the heartbeat, especially in the left lateral decubitus position.  The most common cause of AR in developing countries is rheumatic heart disease; in developed countries it is often due to aortic root dilation or congenital bicuspid valve.

The wide pulse pressure (systolic minus diastolic blood pressure) in patients with AR causes a characteristic "water hammer" or Corrigan pulse: rapid, abrupt upstroke followed by rapid collapse of the peripheral pulse.  AR produces an early diastolic murmur that is high-pitched and sustained or decrescendo in intensity.

(Choice B)  Patients with aortic stenosis have a characteristic pulse with delayed upstroke (pulsus tardus), delayed peak, and small pulse amplitude (pulsus parvus).  Pulse pressure remains normal in patients with aortic stenosis.

(Choice C)  Mitral stenosis occurs most commonly due to rheumatic heart disease.  Patients can have pounding sensations or palpitations due to development of rapid atrial fibrillation.  However, peripheral arterial pulses are reduced in volume and wide pulse pressure is typically not present.

(Choice D)  Pulmonic regurgitation occurs most commonly as a result of pulmonary hypertension or after Tetralogy of Fallot repair in adults.  It does not cause pounding awareness of heartbeat or widening of the pulse pressure.

(Choice E)  Tricuspid stenosis typically presents with right-sided heart failure (eg, elevated jugular venous pressure, hepatomegaly, ascites, peripheral edema) along with clear lungs.  The peripheral pulse pressure would not be increased.

Educational objective:
Aortic regurgitation leads to increased left ventricular (LV) end-diastolic volume due to leakage of blood from the aorta back into the left ventricle.  Features of aortic regurgitation include a wide pulse pressure, "water hammer" pulse, and LV enlargement.  The left lateral decubitus position brings the enlarged left ventricle closer to the chest wall and causes a pounding sensation and increased awareness of the heartbeat.