What is the difference between double cardiac catheterization and cardiac catheterization?

Unknown. I have been performing cardiac catheterizations since my fellowship in 1990-1993 and I have never heard of a 'double' cardiac catheterization. It is possible to perform angiograms of other parts of the anatomy during a cardiac catheterizaiton but you only have one heart. However the cardiologist can perform a right and left heart catheterization instead of just a left heart which is more common.
No such thing. There is no such thing. I suspect you misunderstood what you ere told.