CONFIG_HEARTBEAT is not available for thedefaultarchitecture x86.
Result is shown for architecture sh

Heartbeat LED

modulename: heartbeat.ko

configname: CONFIG_HEARTBEAT

Linux Kernel Configuration
└─>Additional SuperH Device Drivers
└─>Heartbeat LED
In linux kernel since version 2.6.12  
Use the power-on LED on your machine as a load meter. The exact
behavior is platform-dependent, but normally the flash frequency is
a hyperbolic function of the 5-minute load average.

source code: