My cardiologist made an off-hand comment the last time I saw her, when I was asking about ejection fractions. I told her I thought the higher the better (even though I knew better; I wanted to hear her take on it) - she said that some people with much higher ejection fractions might be "running dry," which I took to mean dehydrated. And that maybe being dehydrated increases
ejection fraction.
Did they indicate how much over 70% it was? Because there's a margin of error for those things, too. If you were at 72%, I'd say there's nothing to worry about at all - you have a healthy heart. If it's 95%, then I imagine the doctors will want to run another test or two.
But I'd gauge the relative danger by their reaction - are they bringing you in within the next 48 hours for more tests?