Troponin T (TnT), next to troponin C (TnC) and troponin I (TnI), is part of the troponin complex that plays an essential role in muscle contraction . Even though the troponin complex is present in skeletal and cardiac muscle (but not in smooth muscle), cardiac isoforms of TnT and TnI are tissue-specific and may be distinguished from their skeletal isoforms . These two troponins are released into the bloodstream from myocytes for several reasons, e.g. after long-lasting ischemia of the muscle region . Increased concentration of cardiac troponins is one of the fundaments of the fourth universal definition of myocardial infarction approved by several renowned cardiologist associations . Therefore, recognising cardiac markers (TnT or TnI) in a highly efficient and selective manner is important for diagnosing myocardial infarction. Determination of Kd of isolated peptides enables a qualitative description of their affinity against TnT and, thus, the possibility of application in sensing devices. This paper proposes a mathematical model of interactions occurring during ELISA between a ligand (troponin T) and a non-monovalent receptor (M13 bacteriophage particle exposing TnTspecific peptides). The provided equations enable the calculation of the dissociation constant from ELISA experiments with the critical impact of polyvalency of phage, which was not discussed in any publications previously. The applied method may also cover other systems where monovalent molecules interact with multiple active sites of receptor-like natural antibodies. In addition, the interaction between phage-displayed peptides and TnT molecules was discussed according to their chemical structures.