Many clinical signs compatible with left-sided heart failure also may occur in respiratory diseases, making the distinction difficult in some cases. Dyspnea may be caused by pulmonary edema or pleural effusion, but it may also occur before the patient develops severe fluid retention. Cough is common sign of heart disease in dogs. Dogs with heart disease may cough due to left-sided CHF or due to compression of the left main stem bronchus without CHF. Dogs coughing from pulmonary edema are frequently thin, with severe weight loss and have a more subtle cough that tends to be worse at night, and may be accompanied by pink nasal discharge or sputum. Dogs coughing due to left main stem bronchus compression tend to be obese, have dry, hacking cough that is usually worse during the day.

On physical examination, dogs with left-sided congestive heart failure usually have a fast heart rate, whereas dogs with respiratory disease or left main stem bronchus compression have normal heart rate with pronounced sinus arrhythmia. Presence of a gallop rhythm suggests diastolic dysfunction and heart failure. Crackles may be presented in patients with heart or lung disease, although patients with primary lung disease tend to have louder, high-pitched crackles. Cyanosis can be observed in both primary lung disease and congestive heart failure. Cyanosis in a patient that is not ill strongly suggests that the cyanosis is caused by a respiratory problem. Dogs cyanotic from heart disease usually dye or recover with therapy in a short period of time. Long term cyanosis will be accompanied by polycythemia. Dogs with chronic respiratory disease therefore, have increased hematocrit, whereas dogs with congestive heart failure have low-normal to low hematocrit due to fluid retention. Further diagnostic tests such as chest radiographs, echocardiogram, and tracheal wash may be necessary to establish if the cough is due to pulmonary or heart problem. Careful interpretation of the information obtained in the history and physical examination, however, will allow the veterinary practitioner to arrive at the correct diagnosis with reasonable assurance in many cases.