The agency won the business after a pitch and will service the account from its Cirencester office. It will develop rewards, a launch plan, communications and a strategy for continued growth.
It is understood that the retailer has not had a dedicated CRM agency until now.
Pets at Home works with Krow across its advertising, but the shop is unaffected by the appointment. The brand launched it first TV campaign in 2009. In 2010, it was acquired by the private equity company Kohlberg Kravis Roberts for £955 million.
Scott Jefferson, the marketing director of Pets at Home, said: "EHS 4D demonstrated a real passion for our brand and they were the perfect fit. They have a great track record of engaging people."
Tash Whitmey, the EHS 4D chief executive, said: "Pets at Home have built a strong brand with a fantastic ethos."Follow @SaraKimberley