Malaria parasites degrade substantial quantities of hemoglobin to release heme within a specialized digestive vacuole. Most of this heme is sequestered in an inert crystal. However, the concentration of bioavailable, labile heme in the parasite’s cytosol was unknown. We developed a biosensor to provide the first quantitative insights into labile heme concentrations in malaria parasites. We find that ∼1.6 µM labile cytosolic heme is maintained, including during a period coincident with intense hemoglobin degradation.