Canker Sore Overview. Canker sores, also known as aphthous ulcers, are among the most common causes of painful sores in the mouth. 1  The classic lesion is a small (less than 1 centimeter) oval to round ulcer with a erythematous (red) border.2  They occur on the mucous membranes inside the mouth.anker Sore Overview. Canker sores, also known as aphthous ulcers, are among the most common causes of painful sores in the mouth. 1  The classic lesion is a small (less than 1 centimeter) oval to round ulcer with a erythematous (red) border.
Other Causes of Heavy Panting in Dogs. Heavy breathing or deep, intense panting can also be a symptom of eclampsia, also called milk fever. Eclampsia is a dangerous condition that affects nursing mothers; low blood calcium levels lead to an inability to stand or walk and tremors.
Rapid Heart Rate in Dogs. Sinus Tachycardia in Dogs. Sinus tachycardia (ST) is clinically described as a sinus rhythm (heartbeat) with impulses that arise at a faster-than-normal rate: greater than 160 beats per minute (bpm) in standard sized dogs, 140 bpm in giant breeds, 180 bpm in toy breeds, and 220 bpm in puppies.