Heterophilic antibodies, comprising both "true" heterophilic antibodies and human anti-mouse antibodies (HAMA), represent an important source of interference in laboratory medicine, thus including cardiospecific troponin(s) testing. We describe the case of a 76-years-old woman with implausible and persistent elevation of cardiospecific troponin I, which was finally attributed to interference from heterophilic antibodies. According to literature data, the frequency of this interference ranges between 0.1 and 3.1%, is almost unpredictable and unsuspected, may involve both cardiospecific troponins I and T, and may virtually affect any type of immunoassay, either one- or two-step. The presence of interfering antibodies should always be suspected when test results do not go hand in hand with the clinics, or with the results of additional radiological and laboratory investigations. Once other causes of interference have been ruled out, test repetition with an alternative assay and removal of interfering antibodies with heterophilic antibodies blocking reagent, normal mouse serum, immobilized protein A column or polyethylene glycol may be advisable. As a simple alternative, measurement of serial dilutions of suspected samples usually shows nonlinearity of test results in the presence of heterophilic antibodies.