Rapid and accurate identification of cardiac troponin I (cTnl) in biological fluids is very essential for judging acute myocardial infarction (AMI). Herein, we constructed an enzyme-free electrochemical immunosensing system for sensitive monitoring of human plasma cTnl cardio-cerebrovascular diseases. Prussian blue-doped PAMAM dendrimer nanospheres (PBDENPs) were first synthesized by using in situ chemical reaction, and functionalized with polyclonal anti-human cTnl antibody as the signal-transduction tags. Field-emission transmission electron microscopy (FETEM), dynamic light scattering (DLS), and scanning electron microscopy (SEM) were utilized for characterization of the immunosensing platform. By using a monoclonal anti-human cTnl antibody-modified screen-printed carbon electrode (SPCE) as the immunsensing interface and polyclonal anti-cTnl antibody-labeled PBDENPs and the signal tags, a new sandwich-type immunoassay was designed for the determination of target cTnl by using square wave voltammetry (SWV). Multi-armed dendritic PAMAM nanospheres were expected to enhance the detectable signal of electrochemical immunoassay through the doped Prussian blue with electrochemical activity. Under optimum conditions, the enzyme-free electrochemical immunoassay displayed a wide linear range of four orders of magnitude from 0.01 ng mL⁻¹ to 100 ng mL⁻¹ with a low detection limit of 6.2 pg mL⁻¹ cTnl at the 3s_B criterion. An intermediate precision of ≤10.9% was accomplished with batch-to-batch identification, and good anti-interference capacity against other cancer biomarkers or proteins was acquired toward target cTnl. In addition, measurements of human serum specimens were demonstrated to further confirm the method accuracy of electrochemical immunoassay, and well-matched results were obtained between the electrochemical immunoassay and the referenced enzyme-linked immunosorbent assay (ELISA) method.