Frank Heart, the engineer who oversaw development of the first routing computer for the Arpanet, the precursor to the internet, died on Sunday at a retirement community in Lexington, Mass. He was 89.

The cause was complications of melanoma, his son Bennet said.

In 1969, Mr. Heart led a small team of talented young engineers to build the Interface Message Processor, or I.M.P., a computer whose special function was to switch data among the computers on the Arpanet. To this day, many of the principles Mr. Heart emphasized — reliability, error resistance and the capacity for self-correction — remain central to the internet’s robustness.

Data networking was so new that Mr. Heart and his team had no choice but to invent technology as they went. For example, the Arpanet sent data over ordinary phone lines. Human ears tolerate low levels of extraneous noise on a phone line, but computers can get tripped up by the smallest hiss or pop, producing transmission errors. Mr. Heart and his team devised a way for the I.M.P.s (pronounced imps) to detect and correct errors as they occurred.

Mr. Heart demanded that I.M.P.s be made impenetrable, believing that curious graduate students would be tempted to poke around the machines to see how they worked and bring down the network with their tinkering.