Will a cardiac mri/mra show congested heart failure, blocked arteries, etc? What all will it show?

It Varies. Cardiac MRI will show heart function, valves, and if they give contrast, can show evidence of prior heart attacks. Sometimes it can show blocked arteries, but it's not the best study to look at these.
Maybe. Chestive heart failure best diagnosed with plain chest xray and physical examination. To see "blocked coronary arteries" need sither heart catheterization, or ct angiography, because of ability to see fine detail., speak with your cardiologist to determine which is best for you.
Cardiac MRI. This study is used to look for specific problems. It can show the heart muscle, heart arteries and adjacent great vessels, it can give an indication of function and status of the muscle and valves. Other tests are complementary and your doctor will generally choose what is best to gather the information needed for decision making.
Cardiac MRA/MRI. Yes it will show the blood vessels and show the blockage but if seen on mra the blckage, you will still need angiography for angioplasty or stent placement. It is not a good test for congestive heart failure. You need echocardiogram for that.

Related Questions

Can a cardiac MRI/MRA see blocked arteries? And what does it show exactly?

YES!! A cardiac MRA was designed to show if there are "blocked" arteries... And it is never a replacement for an Angiogram.

Can a cardiac MRI / MRA with contrast done at the mayo clinic see blocked arteries?

Not so well. The test you want is a CTA (CT angiogram), not an MRA. The reason is-MR acquisition is slow and the heart is a moving structure. 64 slice CT is very fast and can capture details despite cardiac motion. (My opinion: the Mayo clinic is the best in the world! Good choice!)