How To Model Heart in Inventor ?

Depending on how detailed you need it I would say open a polygon model and extract either the horizontal edges into nurb curves from top to bottom. This would give a nice detailed solid. The other way might be to creat some geometry based on each of the major parts and the Boolean them to create a complete shape. Once you have that you can go back and start the vascular part that wraps the beast.

Another way might be if you can find a ct scan multi-sclice. Then you could trace the walls and extrude it that way.

Or you can go to Turbosquid and pay for a poly and just go with that. It will probably cost less than the time it takes to make.

Good luck.

What I would do is simple... 2d heart then extrude and fillet.
Wait for it...
Then You can play with the "Fusion Edit Form"
to make it more fancy as per your attached picture!!!
easy peasy

2D heart :
Draw a square with a vertical diagonal
Draw semicircles on two upper edges
Trim all internal lines, and fillet the corners

3D :
Basic : extrude the section by same distance as length of side of square used to draw the 2d, and fillet the edges by half the same distance
i.e if square side = 10, extrude by 10, fillet by 5

Advanced : if you really want this perfect and dont mind working harder.
From your graphic, it is apparent that the edges are not a plain circular fillet, but more elliptical.
Draw the various cross sections, atleast 4, for the upper and lower points, as well as two lobes, and loft the 4 sections using the 2d heart as rail.