ECG Circuit Simulation problems
Without looking at your circuit (unless you post a schematic), at least your parts seem right.  Personally, I'd recommend the AD623 over the INA333 (of course, I don't actually know your specs, so take w/ grain of salt) simply because the inputs on the 623 can actually go a tad BELOW the low rail, which is a huge benefit.  

The way to achieve what you're trying to do is an instrum. amp. stage with V+ as 5V, V- as ground, and Vref as 2.5V.  You'll need to buffer the 2.5V before putting it in to Vref.  A voltage follower there is pretty standard.  The Instr. amp.  should have a modest gain of about 10, to avoid saturating on differences in electrode skin potentials.  The inputs of the amp will go to the two ECG leads, and the ground can go to the leg lead.

After the input stage, you want to filter with a low-freq cutoff of about 0.1Hz and a high-freq cutoff of about 110Hz,  and then an amplifier stage w/ a gain of about 150.  You can build your low-pass into your amp stage, but you should hig-pass before you amplify.