Individuals carrying cardiomyopathy mutations normally have the mutation in one of the two genes and therefore both wt and mutant proteins will be present in the cell. In the case of dimeric protein then homo and heterodimers are likely to exist side by side. We have made α-tropomyosin (Tm) in which one or both chains of the dimer carry a single point mutation associated with dilated cardiomyopathy (DCM). The mutations are E40K, E54K and D230N. Protein unfolding was monitored for a 7 μM solution of Tm (0.5 M KCl, 5 mM MgCl2, 1 mM DTT, 20 mM KPi buffer pH 7.0) using the CD signal at 222 nm with a constant heating rate of 1 °C min−1. The unfolding profile was fully reversible and repeated unfolding curves were superimposable. Each Tm unfolded in via 3 unfolding transitions; those for wt Tm occurred at 40, 47 & 53 °C. The presence of a mutation in a single chain caused a loss of thermal stability with significant unfolding at 37 °C. The least stable transition occurred with a mid-point at 3-5 degrees lower temperature for each of the three Tms carrying a single mutation. The other two transitions were similar to wt for all three constructs. When both chains carried the mutation, the all three transitions were similar to those of the wt Tm. Supported by the Wellcome Trust and a University of Kent Studentship.