home_screen.dart

 @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Example Animations'),
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          firstChild(),
          SizedBox(
            height: 50.0,
          ),
          secondChild(),
        ],
      ),
    );
}

  Widget secondChild() {
    return Row(
      mainAxisAlignment: MainAxisAlignment.spaceAround,
      children: <Widget>[
        Expanded(
          child: AnimatedBuilder(
            animation: _heartAnimationController,
            builder: (context, child) {
              return Center(
                child: Container(
                  child: Center(
                    child: Icon(
                      Icons.favorite,
                      color: Colors.red,
                      size: _heartAnimation.value,
                    ),
                  ),
                ),
              );
            },
          ),
        ),
        Expanded(
          child: Padding(
            padding: const EdgeInsets.only(right: 12.0),
            child: OutlineButton(
              padding: const EdgeInsets.all(12.0),
              color: Colors.white,
              textColor: Colors.black,
              child: Text('Start Beating Heart Animation'),
              onPressed: () {
                _heartAnimationController.forward();
              },
              splashColor: Colors.red,
            ),
          ),
        )
      ],
    );
  }