Hi,
since youre heartrate is not likely to go beyond 255 while you're sleeping, a single reading fits into a byte. You should be able to store all the readings on the arduino itself, since this would a little bit more than 1 kb.
//here we store the data
byte heartBeats[1440];
for(int i=0;i< 1440;i++) {
//Receive the heartbeats for the last 30 seconds from the monitor
beats=WhatverFunctionIsCalledForTheMonitorReading();
heartBeats[i]=beats;
delay(30000); //Wait 30 seconds
}
When you wake up you connect the arduino to your computer and send the data one by one with Serial.Write()
This way you don't have to sleep beside your notebook- (or worse your desktop-) fan.
When you save your data every 30 seconds, you can simply write down the time when you went to bed, otherwise you have to add a real time clock chip to your arduino. (Code for this is somewhere in the playground-section)
Eberhard