signal output from "mega" ,how??????

i need to generate signal from arduino , a signal like sine wave of ECG signal >>> how to do that ??? plz help me

One way: Add an external DAC, such as MCP4901.
Put values in a PROGMEM array, read them out at desired frequency.

:~ :~ :~ sorry tell me how to do that ??? plz more details

any one can help me