Predicted heart mass (PHM) ratio is widely used for donor–recipient size matching in heart transplantation, but its validity in obese patients has remained unclear. A large cohort analysis, using the United Network for Organ Sharing database, published in the Journal of Cardiology, evaluated whether the PHM ratio predicts acute survival across different body mass index (BMI) categories.

The study included 46,141 adult heart transplant recipients. BMI groups ranged from normal weight to obese class II and above, while PHM categories spanned undersized to oversized grafts. Mortality risk increased with severely undersized grafts in normal and overweight recipients but progressively declined with higher BMI. In obese groups, mortality did not vary across PHM categories.

The findings show that the PHM ratio predicts survival in non-obese recipients but not in obese patients. These results suggest that size mismatch poses a minor risk in obesity, supporting expansion of the donor pool and addressing allocation challenges in this growing population.