Heathrow is worse.
Q1) Is this one through (joint) ticket (same question Southam asked)? If it is two tickets - no hope.
If this is one through ticket your luggage gets labelled through to Malta and you get both boarding cards when you check-in at NYC. That way you stay "Airside" and never need to (legally) enter the UK or check in for the second flight. Without that add ~1 hour for immigration plus whatever the minimum check-in time for the second flight = No way.
Q2) Which terminal(s) is this? If you need to change terminals add 30-60 minutes.
Q3) Is your flight going to land on time? What happens if it is 1 hour late? With a through ticket you get a free transfer to the next flight.
As Jennifer says, with a through booking both are tight but possible if everything works. But too tight for comfort. Otherwise no way.