Janet, first of all I'm sorry your brothers didn't come to get you. Shame on them!
A heart cath shows blockage in the arteries taking blood to the heart. They punch a hole in her groin, put a line up to her heart, put in the dye, then look at any blockage there may be. The dye then has to be filtered back out through her kidneys, which you know.
An echocardiogram is used to see if there is damage to the heart muscle itself after a heart attack. It's just like a sonogram. They put goo on your chest and run a doppler wand around on your skin. That's all there is to it.
You may know all of these things already...I'm just trying to help
I love you and I'm so glad your mom can make her own decisions so you don't have to!