Updated

Testimony in the manslaughter trial of Olympic skater Nancy Kerrigan's brother ended Friday after a defense cardiologist said he believes her father's heart began to fail before he and his son got into a physical altercation.

Mark Kerrigan, 46, is charged in the January 2010 death of his 70-year-old father, Daniel Kerrigan, at the family's home in Stoneham, just north of Boston.

Prosecutors allege that it was the physical altercation that triggered Daniel Kerrigan's heart failure. Mark Kerrigan is accused of grabbing his father around the neck with such force that he broke cartilage in the elder man's larynx.

Kerrigan's lawyers say Daniel Kerrigan's heart simply failed after years of coronary artery disease.

On Friday, Dr. Warren Manning, a Harvard Medical School cardiologist, testified as a medical expert for the defense. Manning said Daniel Kerrigan had severely blocked coronary arteries at the time of his death, a condition that could have caused his heart to fail under any number of circumstances, including watching an upsetting football game or, in this case, becoming angry when his son — drunk and yelling — woke him up at about 1 a.m.

"The process probably started when he got angry, got up and quickly went down the stairs," Manning said.

The weeklong trial featured emotional testimony from Brenda Kerrigan — Nancy and Mark's mother — who sobbed as she described the night her husband died. Brenda Kerrigan said she saw her husband and son in a "bear hug" that lasted only seconds before her husband fell to the floor "like a feather coming right out of the sky."

Mark Kerrigan did not testify.

The family has insisted that Daniel Kerrigan's coronary artery disease is what killed him and that Mark Kerrigan is not responsible for his father's death.

Nancy Kerrigan, who was not called as a witness, has been in court every day, often comforting her mother as she cried softly during testimony about her husband's death. The skater said Friday that she and her family would "like it all (to be) over."

The jury is expected to begin deliberations Monday after hearing closing arguments and instructions on the law.

Nancy Kerrigan won a bronze medal at the 1992 Olympics in Albertville, France, and silver at the 1994 Winter Olympics in Lillehammer, Norway. At the U.S. Championships before the 1994 Games, an assailant clubbed her right knee during practice. An investigation revealed that rival Tonya Harding had knowledge of the planning of the attack.