Robert Jerome Zindorf Jr., 84, a former president of an Annapolis heating and air-conditioning business and an enthusiastic sportsman, died Oct. 1 at Maryland Shock Trauma Center in Baltimore of injuries caused by a fall.

He died nine days after falling backward off a guardrail fence at his Queen Anne home while talking to a neighbor. The fall broke his neck and caused spinal cord injuries, resulting in paralysis.

Mr. Zindorf was a fourth-generation Annapolitan and a former altar boy, and a 70-year member of St. Mary's Roman Catholic Church in Annapolis.

After graduating from Annapolis High School, he joined the Coast Guard and served with the "Coast Guard Cavalry," a mounted beach patrol that protected the coastline in Virginia and North Carolina during World War II. During his four-year tour of duty, the cavalry helped capture a German submarine off the coast of North Carolina.

After the war, he returned to Annapolis and became president of J.G. Zindorf & Sons, a heating and air-conditioning business started by his great-great-grandfather, who had delivered coal and kerosene in horse-drawn wagons over the cobblestone streets of Annapolis. He ran the business until 1974, when it was purchased by Eastern Petroleum.

In 1975, he became vice president and chief executive of a newly created subsidiary, Coastal Heating & Air Conditioning, and served in that position until his retirement in 2000. As a businessman, his motto was "Pay attention to detail."

During the 1950s and 1960s, he and his brother Donald were a high-performance boat-racing team that won national championships with the boats Miss Annapolis and Double Eagle. He also was a pilot, an archer, a big-game hunter, a marksman, a breeder of hunting dogs, a cyclist and a marathoner.

A lover of horses his whole life, Mr. Zindorf dreamed of being a jockey as a child and during his senior year in high school wrote a weekly column for the Annapolis Evening Capital called "Boots and Saddles," reporting on horse racing in Maryland. In recent years, he fulfilled his lifelong dream of breeding his own racehorses at Prospect Hill Farm in Upper Marlboro. He had horses that were bred for sulky racing, flat racing, steeplechase, fox hunting, show jumping and Arabian showmanship, and he also bred working Tennessee walkers.

Mr. Zindorf's wife of 49 years, Jeannette Margaret Titlow, died in 1990.

Survivors include his wife of 13 years, Eve Sutton Howard of Queen Anne; three children from his first marriage, Colleen Pierre of Baltimore, Linda Miller of Bonita Springs, Fla., and Janet Zindorf of Greensboro, Md.; two stepchildren, Candace Walter of Odenton and Gary Mintz of Fredericksburg; seven grandchildren; and a great-grandchild.