Researchers at Auckland University say about 4000 patients a year in New Zealand don't get the right treatment for the kind of heart problem they have.
They say the problem relates to a stiffness of the heart and normal treatments don't help.
Researchers from the faculty of medical and health sciences re-analysed information from 29 international research projects, covering 45,000 heart failure patients.
They say heart failure is usually caused by problems with the heart's pumping. But for one in four patients, the failure is caused instead by a stiffening of the heart muscle, often associated with age.
Associate Professor Rob Doughty of Auckland City Hospital says doctors have treated all patients the same until now, and this will have to change.
Cardiac Society chair Andrew Hamer of Nelson says the findings will lead to better methods of treating such patients.