Family and friends streamed in. Detectives scurried about. For Mrs. Smith, the cold realization set in that her oldest son Artie — quiet, shy, car enthusiast, football and softball fanatic — was dead of a heroin overdose.

The death was the end of a particular horror for Mrs. Smith, whose two other children, Mr. Eisel’s younger brothers, also fell into heroin addiction “like dominoes,” she said, and still struggle with it.

To the federal government, which prosecuted the heroin dealers for Mr. Eisel’s death, it was a stark illustration of how Mexican drug cartels have pushed heroin sales beyond major cities into America’s suburban and rural byways, some of which had seen little heroin before.

In Ohio, for instance, heroin-related deaths spread into 18 new counties from 2004 to 2007, the latest year for which statistics are available. Their numbers rose to 546 in that period, from 376 for 2000 to 2003.

Federal officials now consider the cartels the greatest organized crime threat to the United States. Officials say the groups are taking over heroin distribution from Colombians and Dominicans and making new inroads across the country, pushing a powerful form of heroin grown and processed in Mexico known as “black tar” for its dark color and sticky texture.

Their operations often piggyback on a growing and struggling Mexican immigrant population. In a case that provides a window into how this works, two illegal immigrant dealers pleaded guilty to manslaughter last year in Mr. Eisel’s death, in a rare federal manslaughter prosecution from a drug overdose.

Investigators determined that the two immigrants, Jose Manuel Cazeras-Contreras, 30, and Victor Delgadillo Parra, 23, began distributing heroin when they were unable to find jobs. Mr. Parra, in an interview from prison, where he was sentenced to spend 16 ½ years, said he was afraid of being arrested at first, but took the job to support his wife and son, as well as relatives in Mexico.

 “I was living a hard life here in the United States,” Mr. Parra said. “And I didn’t have any other job I was going to go to.”

Another man in the drug ring, who was not directly connected to the death and therefore not charged with manslaughter, was recruited off the streets of Mexico and smuggled into the country expressly to peddle drugs in Ohio, the government said.

Fat on profits made largely in the United States, drug traffickers in Mexico are engaged there in a bloody war among themselves and with the government, which began a crackdown on them three years ago. Since then the violence, including assaults on the police and the army, has left more than 10,000 people dead.

But on this side of the border, the traffickers continue to expand their reach.

Drug Enforcement Administration officials say that Ohio is of particular concern because of the crisscrossing network of freeways here that make it well suited as a transshipment point. Anthony C. Marotta, who heads the agency’s Columbus office, said heroin tied to the Columbus-area dealers had been cropping up in nearby states like Indiana, Kentucky and West Virginia and as far away as the Baltimore area.

The case of Arthur Eisel and the men arrested for selling him heroin shows how the traffickers pushed their product and how in Mr. Eisel, already addicted to expensive pain killers because of a back injury, they found a ready customer for heroin, which was cheaper.

Investigators say that Arthur Eisel was not alone in switching from a prescription painkiller to heroin. It gives a similar, euphoric high at a fraction of the cost, $10 to $20 for a “balloon” — one dose, usually a gram or less — as opposed to upwards of $60 for a typical prescription pill dose on the street.

The traffickers found a ripe market in Grove City, a suburb of Columbus, as they have elsewhere in the nation. Drug seizures ebb and flow over the years, but the amount of heroin confiscated nationwide has been arcing up since the mid-90s, going from 370 kilograms in 1998 nationwide to about 600 kilograms — roughly $150 million worth of heroin — last year, though officials believe it is a small fraction of what is available on the street.

The share of heroin-related prosecutions among federal drug cases in this region has also been climbing, reaching 15 percent of cases last year compared with 4 percent a decade ago.