A doctor who once treated former US President George HW Bush for a heart problem has been shot dead while cycling to work in Houston, Texas.

The Guardian reports that the man who shot and killed Dr Mark Hausknecht at the Texas Medical Center at 9am on Friday morning was also on a bicycle.

Police are now trying to establish whether Dr Hausknecht was specifically targeted, or whether the shooting was a random act.

Troy Finnner from Houston Police said: “The suspect was on a bicycle as well. Rode past the doctor, turned and fired two shots. The doctor immediately went down.”

Dr Hausknecht, aged 65, had been on his way to work at Houston Methodist Hospital when he was shot. He was taken to a nearby hospital for treatment but died there as a result of his wounds.

The suspect was said to have been wearing a gray warm-up jacket together with khaki shorts and a tan baseball cap.

In 2000, Dr Hausknecht, a cardiologist by specialisation, treated Bush for an irregular heartbeat and the former president expressed his condolences to the doctor’s family.

In a statement, he said: “Mark was a fantastic cardiologist and a good man. I will always be grateful for his exceptional, compassionate care.”

Marc Boom, president of Houston Methodist Hospital, said of Dr Hausknecht: “His patients appreciated his kind bedside manner and the extra time he took to answer their questions and fully explain their condition and treatment.

“Our employees who worked with him said patients were so proud to call him their doctor,” he added.