Interstitial pneumonitis is a temporary side effect of sirolimus therapy and has been described mainly in renal transplant recipients. It is considered to be dose dependent and has been documented in patients receiving at least 5 mg daily, or in patients with blood concentration plateaus > 15 ng/ml. In general, clinical and radiologic features improve after discontinuation and, to the best of our knowledge, no reports of fatalities have been published. Our report documents the death in a heart transplant recipient (52-year-old man) that resulted from a loading-dose administration (15 mg), and we report the association of persistently increased blood concentrations (>20 ng/ml) during most of the scheduled administration period.