Wounds of the heart are usually immediately fatal, but sometimes they are not so. The pleurae are very liable to be wounded at the same time. The right ventricle, on account of lying anteriorly, is the part most often involved. The atria lie more posteriorly and are most apt to be wounded in stabs through the back. Not only may the substance of the heart itself be injured but also its blood-vessels. The right coronary artery lying in the atrioventricular groove and the anterior interventricular branch of the left coronary running between the two ventricles anteriorly are the vessels most liable to injury. Owing to the heart being enclosed in the pericardium, - a closed sac, - if blood accumulates in it the action of the heart is interfered with. To avoid this occurrence, wounds bleeding externally should not be closed, or distention of the pericardium may ensue.

Fig. 221.   Percussion area of the liver and heart. The light shaded area represents the extent of deep or relative dulness and the dark shaded area that of superficial or absolute dulness.

Fig. 221. - Percussion area of the liver and heart. The light shaded area represents the extent of deep or relative dulness and the dark shaded area that of superficial or absolute dulness.

Wounds of the heart have been sutured successfully. In order to reach the heart, a portion of the chest-wall would have to be resected and turned to one side as a flap. This will probably require the opening of the pleural cavity. The pleurae will in all likelihood already have been involved and found to be filled with blood, as has occurred in at least one case.

A knowledge of the exact outlines of the heart as already given will often enable one to decide as to whether a wound involves the heart or not.