The intravenous version of Cardiome's flagship product is sold as Brinavess IV and is approved in Europe for treating abnormal heart rhythm in adult patients.
The companies said that they will work together to ensure a smooth transition and continued availability to doctors and patients in countries where the medicine is approved.
"We have made a business decision to return the rights for Vernakalant to Cardiome," said Michael Mendelsohn, head of atherosclerosis and cardiovascular research at Merck Research Laboratories.
"We continue to support the safety and efficacy profile of vernakalant. We look forward to working with Cardiome to conduct a transition that has the best interests of patients and their physicians in mind."
Earlier this year, Cardiome slashed 85 per cent of its workers after Merck said it was terminating development of the oral version of vernakalant.