Patients with thyreotoxicosis have variable clinical manifestations and various degree of cardiomyopathy which severity depends on many factors. Last years the genetic factors predicting development and clinical features of thyrotoxic symptoms and thyreotoxic cardiomyopathy became more evident. It is known, that production of T3 in various tissues including cardiac muscle is limited by deiodinase 2 (D2). Recent studies showed that certain polymorphisms, including Thr92Ala of D2 gene, are implicated in the development of thyrotoxic symptoms and thyreotoxic cardiomyopathy. Individuals with Ala92Ala genotype have lower D2 activity in tissues compared to other genotypes. In our study we focused on codon 92 polymorphism of D2 gene in relation to clinical manifestations of thyreotoxic cardiomyopathy and Echo-cardiography parameters in patients with Graves' disease.