Cook the rigatoni according to package instructions until al dente.
In a large skillet, melt the butter over medium heat and sauté the garlic until fragrant.
Add the diced chicken to the skillet, seasoning with salt and pepper. Cook until the chicken is browned and no longer pink inside.
Pour in the heavy cream, stirring to combine, and bring to a gentle simmer.
Stir in the grated Parmesan cheese until melted and smooth, adjusting with reserved pasta water if necessary.
Add the cooked rigatoni to the skillet, tossing to coat in the sauce.
Taste and adjust seasoning as needed, then garnish with fresh parsley before serving.
