I thought this was a tough question -

I might be really off here, but I'm going to rule out cardiac tamponade, constrictive pericarditis, and restrictive cardiomyopathy because Kussmaul's sign is absent.

Now that leaves me with congestive heart failure and an MI. I would expect a big heart in CHF.

So that leaves me with an MI. My reasoning might suck so feel free to refute my answer.