HD is recorded to P2 cards only, Zackfilms. You can downconvert HD to mini-dv tape in Standard Definition format. SD cards are only used for saving/loading scene files and user files.
It sounds like the question was about recording onto the SD card. The HVX can record only onto P2 or tape. The SD card is only for storing scene files and metadata. And as David said, high defintion can only be recorded onto P2 cards.