I felt it merely needed 2 'more' springs added on the 2 stems of the heart plunger mechanism, either that or tension (stretch) the main solenoid spring.

MM

1812 is the new addition. Need to do a bit of work to the heart as the rubber has lost most of it's elasticity and doesn't pull the solenoid back up. the spring is strong enough but the heart just sags so I might try a light bit of spring metal or plastic to reshape it.