In the lateral view, thoracic spine is straight and the distance between the sternum and the vertebrae is reduced to 10 cm or less.

This straight back syndrome may cause the area of the heart in contact with the sternum anteriorly to increase. In more extreme cases, this may cause distortion of the silhouette of the heart and great vessels. Straight back syndrome and other thoracic and skeletal abnormalities, such as pectus excavatum and mild thoracic scoliosis may occur in association with mitral valve prolapse.