Sascha Vergin, 37, was fitted with the device when he was just 19.
It was made by Berlin-based company Biotronik, which has a UK office in Bicester.
Sascha, who was champion of his cycle club last year, regularly takes part in races and travels more than 6,000 miles annually on his trusty two wheels.
He said: “Thanks to my pacemaker I can continue to enjoy exercising. My English friends always talk about how beautiful the countryside is here, so we decided to do a bike tour of the area.
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“The fact that Biotronik has an office in Oxfordshire was another reason to visit – and I wanted to do something good at the same time so combined it with fundraising.”
Sascha was joined on the British leg of his 400 mile charity challenge by friends Joshua Skinner, Richard French and Dom Vizor.
The team raised money for the Children’s Heart Centre in St Augustin, near Bonn and finished their tour at Biotronik’s Bicester office.
Company spokeswoman Amy Wright said: “Sascha is an inspiration and a great role model for our patients – especially those wishing to get more active.
“He shows that having a cardiac problem doesn’t have to to hold you back and we congratulate him on completing this epic journey.”
Cardiac physiologist Paul Charlton said: “Cycling – more than any other physical activity – is a challenge in programming heart rate response for cardiac device patients. His journey is a true testament to the flexibility and quality of the device.”