Crossing a pug with a Shih Tzu results in a mixed breed dog known as the pug-zu. Since this "designer dog" isn't a purebred, puppies might look like a combination of both parents or favor one parent's appearance over the other. The two breeds are both brachycephalic, meaning short-headed, so one guarantee is a short-nosed dog. Both breeds originally hail from China. Expect your pug-zu to share your life well into his teens.
The pug's breed standard doesn't specify a height, but adult dogs should weigh between 14 to 16 pounds. The Shih Tzu breed standard specifies a weight of between 9 to 16 pounds, standing between 8 and 11 inches tall at the shoulder. Expect your pug-zu to mature somewhere in that range, and not weigh more than 16 pounds. That, of course, assumes you feed him a high-quality dog food and don't overdo the treats. Since neither breed requires a lot of exercise, it's easy for them to pack on pounds with overfeeding; that's especially detrimental to this hybrid dog's health.
Both the pug and Shih Tzu are square, compact and short-legged, so that's your pug-zu's basic body structure. He could inherit the shorter ears of the pug or the slightly longer ears of the Shih Tzu parent. Pugs appear in fawn and black, the former with a black mask. The Shih Tzu comes in virtually any canine shade. The pug's coat is short, requiring minimal upkeep. The Shih Tzu boasts a long, double, flowing coat -- and the upkeep is far from minimal. Your pug-zu might inherit an in-between, medium-length coat. Many pug zus have the facial hair characteristic of Shih Tzus.
Your pug-zu should boast a good temperament, as both breeds are sweet, loving canines. They do well with older kids, other dogs and felines. Neither breed was developed for any purpose other than companionship and affection, and they do that very well. Your pug-zu might be a good watchdog, for his size, but his Shih Tzu heritage might result in too much barking. A few daily walks are sufficient for exercise, but avoid anything other than brief potty breaks in hot weather. Their short noses result in breathing difficulties when the temperature climbs.
The facial structure of the pug-zu is responsible for many potential health problems. As noted, they are prone to respiratory issues, and might require surgery to enlarge their nostrils or reduce an elongated soft palate. Both breeds are prone to slipped kneecaps, which also can require surgical correction. Pugs and Shih Tzus are predisposed to eye disorders, partly a result of shallow eye sockets. These eye problems include cataracts, dry eye, progressive retinal atrophy and corneal ulcers. You might want to find a veterinary ophthalmologist to examine your dog annually, in addition to wellness visits with his regular vet.