Heart sounds. A. Normal. S₁, first heart sound; S₂, second heart sound; A₂, aortic component of the second heart sound; P₂, pulmonic component of the second heart sound. B. Atrial septal defect with fixed splitting of S₂. C. Physiologic but wide splitting of S₂ with right bundle branch block. D. Reversed or paradoxical splitting of S₂ with left bundle branch block. E. Narrow splitting of S₂ with pulmonary hypertension. (From NO Fowler: Diagnosis of Heart Disease. New York, Springer-Verlag, 1991, p 31.)