SANTA ANA -- A Garden Grove man of Vietnamese descent got so angry at his 71-year-old mother for nagging him to become a doctor that he choked her, causing her to have a fatal heart attack, a prosecutor told jurors Thursday.

Son Richard Lam Nguyen, 31, is on trial for the murder of his mother, Nuong Nguyen, on Dec. 20, 2008.

His attorney, Rob Harley told the jury he is not guilty of murder because he choked his mother in the "heat of the moment,'' and that her death was an "accident'' not caused by choking.

Son Nguyen had a close relationship with his mother, who paid for his schooling until the night of her death, when she gave him an "ultimatum,'' as Nguyen told police, to become a doctor instead of a pharmacist.

The argument "escalated'' as Son Nguyen said it made more sense to finish the last year of school he needed to become a pharmacist instead of the six years he would need to become a doctor, Harley said.

Nuong Nguyen said he would shame the family if he were to be a pharmacist and cause her to "lose face'' with her best friend whose two sons were doctors, Harley said.

Since it was rare for the two to argue, the confrontation shocked the son into "going ballistic,'' and he choked her for six to seven seconds, Harley said.

Son Nguyen ran out of the house, with his mother still gasping for breath, and drove around for a few hours until he fell asleep, Harley said. At some point, he grew worried that his sickly mother, who needed dialysis for a bad kidney and suffered from anemia and a weak heart among many other ailments, may have died, Harley said.

When Son Nguyen arrived home, he found his mother dead, called police and told investigators what happened.

Deputy District Attorney Cameron Talley played portions of a video in which Son Gguyen calmly told an investigator about the dispute with his mother and how he choked her.

"She just kept nagging, and I turned around and put my hands on her neck and squeezed real hard for six or seven seconds,'' he said and acknowledged that what he did was "illegal.''

Talley said the evidence will show Son Nguyen choked his 5-foot, 80- pound mother with such force that it broke the vertebrae in her neck and some thyroid cartilage.

"He took his hands, put them around her frail, wrinkly throat and squeezed really, really hard,'' Talley said.

He asserted the choking triggered a fatal heart attack.

Talley acknowledged that Son Nguyen has a history of mental illness, but noted he was prescribed drugs that helped him earn a degree in biology from UC Irvine and go on to a pharmaceutical school in Massachusetts and medical school at Ross University in the Caribbean country of Dominica.

Son Nguyen had no other mental health issues until January, when he was about to go on trial for murder, Talley said.

Harley said the case is "about a mother's lifelong obsession with having a doctor for a son,'' Harley said.

He said mother and son had a close but "dysfunctional'' and "co- dependent'' relationship, and that she told Son Nguyen to spy on his father when she suspected he was having an affair. They later divorced.

Confrontations with his father led to Son Nguyen being hospitalized for his psychological problems, Harley said.

Harley said he intends to show how Vietnamese cultural issues played a part in his mother's badgering her son about his career choices. He said it is not uncommon for some Vietnamese parents to pick a career for their children and then expect them to follow through or face humiliating shame.

Son Nguyen suffered from schizophrenia, anxiety and depression and his mother "was a heart attack waiting to happen,'' he said.

"He was constantly dealing with the fear of not living up to his mother's expectations,'' Harley added.

The two lived together in a rented room in Garden Grove, and Son Nguyen had to take a year off from school because her medical issues had drained their finances, Harley said.

Son Nguyen thought it was more practical to do one more year of school and get a job as a pharmacist to help his mother with her medical bills, Harley said.