When the Roman soldiers approached Jesus on the cross intending to break his legs, they found he was already dead (v33). Indeed, he had been observed to die by eye witnesses a short time before (v30). Seasoned executioners such as these were unlikely to be mistaken in their diagnosis and the observation of 'a sudden flow of blood and water', when Jesus' side was pierced by a sword, confirmed the fact (v34).

Post mortem clotting of the blood can be delayed by the presence of circulating fibrinolysins, especially if death is associated with severe pain. The effect is that the red cells can separate from the plasma within thirty minutes. 'Blood and water' would then emerge in sequence by gravity from a body cavity pierced by a sharp object.

The only real possibilities for the source of the blood and the water are the pleural and pericardial cavities, because the heart itself contains too little. Haemothorax could well have resulted if ribs had been fractured during the flogging Jesus received in Pilate's palace (Jn 19:1). Haemopericardium could have resulted from either cardiac rupture or, more probably, rupture at the junction of aorta and left ventricle.

Luke favours haemopericardium on the basis of the prophecies that none of Jesus' bones would be broken. (Ex 12:46; Nu 9:12; Ps 22:17, 34:20; Jn 19:36)