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The effect of a high-frequency alternating magnetic field on HeLa tumor cells incubated with ferromagnetic nanoparticles of manganese oxide perovskite La_0.56(SrCa)_0.22MnO₃ have been studied. The particles were subjected to a size selection process and coated with silica to improve their biocompatibility. The control assays made with HeLa tumor cells showed that cell survival and growth rate were not affected by the particle internalization in cells, or by the electromagnetic field on cells without nanoparticles. However, the application of an alternating electromagnetic field to cells incubated with this silica-coated manganese oxide induced significant cellular damage that finally lead to cell death by an apoptotic mechanism. Cell death is triggered even though the temperature increase in the cell culture during the hyperthermia treatment is lower than 0.5 °C.