"But when they came to Jesus and found that he was already dead, they did not break his legs. Instead, one of the soldiers pierced Jesus’ side with a spear, bringing a sudden flow of blood and water. The man who saw it has given testimony, and his testimony is true." (John 10:33-35).
Roman soldiers were trained in delivering a fatal wound. This type of chest stabbing appears to have been a matter of protocol, particularly if the body were to be released for burial. It was a kind of coup de gras, assuring the victim was finally and actually dead.
It has been suggested that Jesus died by this stab wound. There is logical merit to this suggestion, since it would produce immediate death, as well as provide a description consistent with the biblical account.
It seems the Jesus developed a pleural effusion (fluid around the lungs). A pleural effusion could occur by heart failure, or from blunt trauma to the chest wall from beating and scourging. A spear entering the chest cavity would first tap this fluid, causing the appearance of water flow. The spear would then enter the right side of the heart, causing blood flow from the chest wound.
Based on the supposition that blood cannot flow from a corpse, some have considered this stabbing to be the means of Jesus' demise. However, blood clotting can be irregular, clots can again return to a liquid state (liquifaction), and physiologic mechanisms of blood clotting can be diminished with traumatic shock. The description of blood flowing from Jesus' chest wound does not mandate the conclusion that he was alive at that moment.
The Roman soldiers performing crucifixions would have credible expertise in pronouncing death. The soldiers found Jesus to be dead prior to delivering the stab wound. The biblical description therefore does not support the fatal stab wound hypothesis.