Henry Patterson Loomis (April 29, 1859 − December 22, 1907) was an American physician. He was born in Manhattan and attended Princeton, graduating in 1880. He received his medical degree from New York University in 1883, and studied in Germany before returning to the U.S. in 1887. He married Julia Stimson on February 9 of that year, and they had three children, Julia Atterbury Loomis, Alfred Lee Loomis, and Henry Loomis, who died of rabies while still a small child; he was bitten by a rabid dog on the street near the family's house in Manhattan.
He was a leading expert on heart and lung diseases.
In the summer of 1907, Loomis's wife filed suit for divorce, claiming that Emilie Grigsby, an heiress of the estate of Charles T. Yerkes, had a relationship with Loomis. The family were snubbed socially as a result, since a divorce was regarded as a shameful event.
Loomis was professor of pathology at New York University and was also a faculty member of Cornell University. He died on December 22, 1907, of pneumonia, at his home in Manhattan before the divorce went through.