With regards to the echo boards, there are two classifications: testamjur and certified. A testamur has taken and passed the written exam. Someone certified has passed the written exam and fulfilled further requirements to become certified. There are 2 ways to become "certified." One is the fellowship pathway, and the other is the practice pathway. The fellowship pathway will be the only way to become "certified" if you finish your residency training after June 30, 2009. Case numbers per se is not the issue. If you want more details as to what is required for certification, check out the PTEeXAM application at
http://echoboards.org.
The other issue is what the group wants. Do they want someone who has formal fellowship training or just someone with experience. Different groups will have different wants. I know some where they're more interested in experience and others that require a fellowship. If you really want to do hearts anywhere, a fellowship will give you the credentials to do it. Whether it's truly needed is another story.