I have had psvt's with heart rate over 250 twice, but i have had cardiac ablation 4 yrs ago. what does this mean?

Repeat ablation?: Sometimes svt's require more than one ablation to cure them. Alternatively you could be having a different type of arrhythmia. I recommend getting back in with your ep for a full evaluation.

A few possibilities: It is possible that your procedure was initially successful, but that the result has not been sufficiently durable. This occurs, generally, less than 10% of the time but is possible. Another possibility is that you have developed a new arrhythmia other than the one for which you are originally treated. A consultation with an electrophysiologist is advised.