Application Pool Defibrillator (APD) is a simple application built with the .NET Framework to enhance your ASP.NET application's performance with the goal of reducing initial page load times by keeping the IIS application pool / worker process alive.
APD operates on the concept that by default most application pools are set up to shut down their worker process after a predefined amount of idle time generally 15-20 minutes. If traffic to your site is constant and predictable simply increasing the idle timeout value can resolve your problem, but for smaller sites, sites where traffic is lower and less predictable, or where the site owner does not have access to IIS settings, APD can be a valuable tool that can significantly increase the performance of your site by simply reducing the initial page load time.