Mark Kerrigan is on trial for manslaughter in the death of 70-year-old Daniel Kerrigan.
Dr. Henry Nields said he believes Daniel Kerrigan's fatal cardiac dysrhythmia - a loss or interruption of a normal heartbeat - was brought on by the altercation. Nields also said Daniel Kerrigan had an acute fracture of cartilage in his larynx, an injury prosecutors say Mark Kerrigan inflicted.
Mark Kerrigan's family, including Nancy Kerrigan, supports him. They say Daniel Kerrigan died because he had severe blockage of his coronary arteries.
Nields says he believes Daniel Kerrigan's heart disease played a role in his death.