Medical transcription requires speed and accuracy. Both qualities are needed for having an "A"-result transcribed document; well, basically, if not perfectly. It is frustrating sometimes when these two qualities are not achieved immediately. Patience is required or else the medical transcriptionist would feel depressed, thus discouraging him further to improve such qualities.
Transcription can be done with ease. It must be done heartily too. It must be done without "dwelling" so much on terms that cannot be deciphered or heard for the first time. Transcribe lightheartedly, keeping in mind that re-listening to the dictation, having somebody hear them, or researching for the terms will also do the trick of solving such indecipherability. If you come to such terms that you cannot understand, flag them first by putting a blank or highlighting it. Continue transcribing until you have reached the end of the dictation file.
When you're done doing that, go back to the terms you've missed or flagged. You have three options now: re-listening to the file (this one is a must though), having somebody hear them for you, or researching the terms. Doing so, those flags or blanks can be filled in. If all else fail, leave them in a blank format. It is safer that way than having to fill them with terms that you are not sure of or that you thought that you have heard them right. Chances are, you heard wrongly. If you heard them right, they wouldn't have been flagged in the first place!