Analysis of the cardiovascular manifestations caused by loss of thoracic kyphosis has been incomplete. Accordingly, this study was designed to investigate the physical signs and the electrocardiographic, radiologic, hemodynamic, and pulmonary ventilatory features of this skeletal defect. Twenty-three patients with straight thoracic spines in lateral chest x-rays were selected. Ratios of anteroposterior to transthoracic dimensions were uniformly below a mean derived from 100 normal subjects. Cardiac features included pulmonic ejection murmurs, palpable left parasternal systolic impulses, loud delayed sounds of tricuspid valve closure, exaggerated respiratory splitting of the second heart sound, vertical electrical axes, rSr′ patterns in leads V1or aVR, radiologic prominence of the pulmonary arteries, levodisplacement of the heart, a “pancake” cardiac configuration simulating cardiomegaly, occasional alterations in height or contour of the right ventricular diastolic pressure pulse, and an occasional mild pulmonary ventilatory restrictive defect. Differential diagnoses principally included atrial septal defect, mild pulmonic stenosis, and idiopathic dilatation of the pulmonary artery.