"Information Resources on Swine in Biomedical Research" notes that pig hearts share the following features with those of human beings: they have four chambers, two for poorly oxygenated blood and two for oxygenated blood and are approximately the same size in both species for an individual of similar weight. Both species have a vaso vasorum and the blood supply to the heart in both is dominated by the right artery.
Pig bodies also handle fats in a similar way to human bodies, which is important as fatty plaques are a contributor to heart disease in both species. This makes them an excellent model for studying coronary heart disease in human beings.
Pig hearts are not exactly the same as human hearts. The fetal pig dissection guide highlights one notable difference: pigs have a large vessel to the rear of the heart from which blood from both the heart and the left chest wall is drained. In human hearts, there is a vessel called the azygous vein that supports the left cardinal vein in draining blood from the heart. Pigs do not have an azygous vein, and consequently, their cardinal vein is very large and drains blood not only from the heart but from the chest itself.
As noted in Simon J. Crick's paper, pig hearts also differ from human hearts in shape, texture and the angle of the blood vessels. Human hearts have a rectangular profile, while pig hearts have more of a rounded "heart" shape. Pig heart muscle is coarser and more friable; pigs also have two fewer orifices in their left atrium than human beings.