(CNN) -- A forensic pathologist testified for the defense in the George Zimmerman trial Tuesday, describing Trayvon Martin's traumatic last moments alive as he bled to death in the grass after being shot at close range.

"If he was involved in a struggle you expect his heart to be going, beating -- especially after he had been shot -- more than a 100 times a minute," said Dr. Vincent Di Maio, adding that the way Martin died supports Zimmerman's version of the shooting.

"You are losing 1,500 cc's {cubic centimeters) in a minute. That's about a quarter of his blood supply. In a second minute, if you can assume the same rate. Actually the heart would probably be beating faster for the second minute. He is going to lose another 1,500. Well that means he has lost more than 50%of his blood supply."

Zimmerman, who's on trial for second-degree murder in Martin's death, appeared to be paying close attention during the testimony. Tracy Martin, the victim's father, was in attendance but didn't show much emotion as he heard the details of how his son may have died. Trayvon's Martin's mother, Sybrina Fulton, was not in attendance.

Di Maio said, given that the entry point of the bullet was a "contact wound" -- meaning at close range -- Trayvon Martin never had a chance. "In this case you have a through-and-through hole of the right ventricle, and then you have at least one hole if not two into the right lung. So you are losing blood, and every time the heart contracts, it pumps blood out the two holes in the ventricle and at least one hole in the lung."

Di Maio also said Martin's gunshot wound indicates the gun was up against the teen's clothing, about 2 to 4 inches away from the skin. He also said the weight of the canned drink in Martin's hoodie pocket may have been pulling his clothing away from his body by a few inches if Martin was on top of Zimmerman, as the former neighborhood watch volunteer has claimed.

In any event, "He is going to be dead between one and three minutes after being shot," said Di Maio.

Seventeen-year-old Martin had been walking through the Retreat at Twin Lakes -- the gated community in Sanford, Florida, where Zimmerman lived -- on February 26, 2012, when the two got into a physical altercation. Zimmerman told the police he shot Martin in self-defense while holding the gun in his right hand at point-blank range. He said the teenager was on top of him at the time. Di Maio said the medical evidence is consistent with how Zimmerman has described shooting the teenager.

Di Maio explained to the jury Tuesday that Martin may have lost consciousness between 10 and 15 seconds after being shot, and may have been able to talk or make voluntary movement during those last seconds. This appears to support Zimmerman's claim that Martin said, "You got me," after being shot.

Before testimony began Tuesday, Judge Debra Nelson held a hearing on the admissibility of a 3D animation -- commissioned by the defense -- of the altercation between Zimmerman and Martin.

Animator Daniel Schumaker, testifying outside of the presence of the jury, said that he uses crime scene evidence and the same motion capture technology used in movies like "Iron Man" to design his digital re-creations of alleged crimes.

The hearing on the animation will resume at the end of testimony Tuesday.