Heart attacks, strokes and death were more common in patients whose weight changed the most over four years.
For some patients, weight changes might have reflected yo-yo dieting, which some previous studies have suggested may be unhealthy for people without heart problems. That means a hefty but stable weight might be healthier than losing but repeatedly regaining extra pounds.
But big weight fluctuations in heart patients studied could also have been unintentional and a possible sign of serious illness that would explain the results.
Experts say more research is needed on potential risks of yo-yoing weight.
The study was published Wednesday in the New England Journal of Medicine.