Beck's triad (cardiology)
1: The rising jugular venous pressure is evidenced by distended jugular veins while in a non-supine position. It is caused by reduced diastolic filling of the right ventricle, due to the outside pressure being exerted on it by the expanding pericardial sac. This results of a backup of fluid into the veins draining into the heart, most notably, the jugulars. In severe hypovolemia, the neck veins may NOT be distended.
2: The fall in systolic pressure results when the fluid in the pericardial cavity accumulates to a degree that it impairs ventricular stretch, thus reducing stroke volume and cardiac output.
3: The suppressed heart sounds occur due to the muffling effects of the sounds passing through the fluid surrounding the heart.