oops! I found it. in a normal myocardium K1 would be around 0.7 in k2 would be something like 0.17.
How do you know that two exponential terms is not a one-compartment model? The equation is the same; biexponential. For that matter, how do you know that two-exponential terms fit the concentration curve efficiently, or, has anything to do with myocardium.? Why should an instant starting volume be considered "real"? If you assume an instant mixing model, K1 and K2 will reflect the mixing assumption, and not very well reflect myocardial physiology. This is a well known problem, that the coefficients of sums of exponential terms do not reflect anything in particular, and that one adds compartments merely to fit the data better, not because one patent has one compartment and the next has three.
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In addition to the aforementioned complexities, K1 varies vastly for different (radio)-tracers which are linked to the clinical target, namely the myocardial blood flow - if one uses the Renkin-Crone equation K1 = E*MBF, E = (1-exp(-PS/MBF)). In other words, for a normal MBF of 0.8, K1 could be 0.8 for 15-O water, 0.75 for N-13 ammonia or 0.5 for 82-Rb (numbers gut feeling...) - depending on the extraction fraction (E) of the particular tracer.