.mat files always contain named variables, not just pure data. There may be several variables in one .mat. We do not know which variable to load (you did not specify), so we will assume that the first variable in the list is the one to load. If there is only one variable then it would be the first.
datastruct = load('TheFileNameHere.mat');
varnames = fieldnames(datastruct);
var_to_load = varnames{1};
imagedata = datastruct.(var_to_load); %pull out the data for that variable
imagesc(imagedata); %view it
