In a medium bowl, mix together cake mix, soda, oil, eggs and syrup until well-blended and uniform. Fold in maraschino cherries.
Coat the insides of 6 heart molds with nonstick spray (or you can use silicone baking cups).
Divide batter evenly between molds and seal each with aluminum foil.
Pour one cup of water in the Instant Pot and insert the steam rack. Carefully lower the molds on to the steam rack--3 on top, 3 on bottom, staggering the layers.
Secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- keys and program the Instant Pot for 15 minutes.
When the time is up, let the pressure naturally release for 10 minutes, then quick-release the remaining pressure.
Carefully remove the molds from the pot to a wire rack. Remove foil and allow to cool for 5 minutes.
Meanwhile, in a small bowl, mix together powdered sugar and enough milk to form a thick but pourable icing
Remove the cakes from the mold and drizzle icing into the heart-shaped depression in the top of the cakes. Top each cake with an additional cherry.
Notes
*The MANUAL and PRESSURE COOK buttons are interchangeable.