First of all, tempo is the same for all your instrument. BPMs is the speed of tempo. If your drum kit is in 4/4 time signature (that means you have 4 hits, usually count with hi hat, in every meter) and you want half of those notes on your bass, that mean you have 2/4 on you bass. This is very simple thing to do, you have to imagine that you split up at half every bass note (always at your 2/4 TS). Now you have count your hi hats, two hits on each bass note, and you similarly can place the other components of the kit.
Now, in your 'where' question. Always in 4/4 time signature meters you have two strong and two weak hits. The first one and 3rd one (like Tim said) are strong ones, the other two are weak. We always put kick and snare on strong for emphasis, but you can always extend kicks and snare to weak parts too.
However, in other time signatures meter we have different strong and weak hits, for example in 3/4 we have 1 strong (at hit one) and two weak).
So, now you have to figure out how your rhythm going on, if you want heart beat kind of rhythm you have two notes on 1 and 2 on your beat and pauses (nothing, silence) on 3 and 4. Don't forget that you bass can play either 1/4 value notes either 2/4 value notes, just remember that if you are going with 2/4 TS means that 1 and 2 beats are a single bass note and same for 3 and 4. You just need to experiment with those and find out, I think heart is beating 60 times per second, so if you want to simulate this you may want to change bpm at 60 (at 4/4) or even 120, if you want your drums a bit faster.
Conclusion: same bpm, same time signature but adapt the way you count it in every instrument (depend on rhythm), figure out rhythm and ready to go.
Sorry for my bad english, I hope I helped you, enjoy writing music.