This is a flathead from an old GM inline-six engine. Looking up from the bottom of the head, the heart-shaped lobes to the left allowed clearance for valves opening up from the engine block below, forming part of the combustion chamber, which extends to the right over part of the cylinder. You can still see the silhouette of each cylinder to the right of the combustion chamber. Because of the void in a flathead like this, which allows for valve clearance, the compression ratio is relatively low. Compression can be raised by milling the head thinner (and thus making the combustion chamber smaller) but only so much since the head gets weaker and the valves still need to clear it when they are open.