Los Angeles- Actor Chris Penn’s sudden death at age 40 last month was caused by a deadly heart condition, though a commonly prescribed cough syrup probably was a contributing factor, the Los Angeles County coroner’s office said Monday.

Investigators found that Penn died of “nonspecific cardiomyopathy” – a disease of the heart muscle that is usually fatal over time. Penn’s heart was enlarged, weak and “could have given out at any time,” said coroner’s spokesman Craig Harvey.

But investigators also found that the effects of multiple medications were a “significant condition” contributing to Penn’s death. They highlighted one prescription medication in particular – Phenergan, a commonly prescribed cough syrup that contains an antihistamine but is not typically considered dangerous in adults, according to doctors.

Harvey said the cough syrup, which also has codeine in it, played a role in Penn’s death, but was “not a direct cause.”

Penn also had other legal medications in his system, though Phenergan was the only one specifically identified by investigators Monday as a significant factor in the case. No illegal drugs were found, they said.

Cardiomyopathy is a progressive disease that weakens and scars the heart muscle, said Dr. Gerald Pohost, chief of cardiovascular medicine at USC’s Keck School of Medicine.

“It may take months, years or decades, but it usually leads to the patient’s demise,” he said.

Although Phenergan “doesn’t cause heart failure,” Pohost said, its sedative properties could increase breathing difficulties in obese patients and strain a heart already weakened by cardiomyopathy. Penn, a hefty character actor who played thugs and cops in a career spanning several decades, was 6 feet 2 and weighed 310 pounds.

He was found lying unresponsive in his bed by a housekeeper in his Santa Monica condominium Jan. 24. Coroner’s investigators believe he died sometime the previous day, Harvey said.

He declined to give further details of autopsy and toxicology tests conducted by investigators pending the release of the coroner’s official report on Penn’s death.

Harvey said he did not know exactly how much Phenergan had been ingested by Penn.

But, he said, investigators found that the actor had a prescription for the cough syrup filled three days before his death, and that the bottle was one-quarter full when he died.

Primarily, Penn “just had a bad heart,” Harvey said.