From Death Note Animé Series

Text:

The human whose name is written in this note shall die.

This note will not take effect unless the writer has the subject's face in their mind when writing his/her name. Therefore, people sharing the same name will not be affected.

If the cause of death is written within 40 seconds of writing the subject's name, it will happen.

If the cause of death is not specified, the subject will simply die of a heart attack.

After writing the cause of death, the details of the death should be written in the next 6 minutes and 40 seconds.