Many of the drugs used to treat heart disease in animals are the same medications used in people (see Drugs and Vaccines: Commonly Used Cardiovascular Drugs*).
Positive inotrope drugs increase the strength of the heart muscle by increasing the amount of calcium available for binding to muscle proteins. Increasing the amount of available calcium is done in different ways depending on the drug used. There are 3 classes of positive inotropes: cardiac glycosides, beta-adrenergic agonists, and phosphodiesterase inhibitors.
Angiotensin-converting Enzyme (ACE) Inhibitors
Angiotensin-converting enzyme (ACE) inhibitors are widely used to treat chronic congestive heart failure in dogs and cats. When angiotensin-converting enzyme formation is prevented, the narrowing of the blood vessels that is common in dogs with congestive heart failure is prevented. It also helps reduce the buildup of sodium and water in the body, which is another side effect of congestive heart failure. The use of these inhibitors helps increase the output of the heart and increases the animal's ability to exercise safely.
Vasoactive drugs dilate or widen the blood vessels. There are 2 types of dilators. Arterial dilators are drugs that dilate the arterioles, which makes it easier for the heart to pump blood away from itself. Venous dilators dilate the veins coming to the heart and increase the amount of blood that enters the heart.
Antiarrhythmics help the heart beat in its normal, rhythmic pattern. There are 4 classes of antiarrhythmics, grouped according to how they affect the heart cells. Class I drugs work to fix irregular heart rhythms and abnormal heart beats. Class II antiarrhythmics work to prevent irregular heartbeats and block the effects of hormones (such as adrenaline) on the heart. Class III antiarrhythmics have no practical applications in veterinary medicine. Class IV drugs are referred to as calcium antagonists or calcium-channel blocking drugs. These work in the same way as Class II drugs.
Hematinics are drugs that increase the amount of hemoglobin (the portion of the red blood cell that carries oxygen throughout the body) and the number of red blood cells in the blood. These are used to treat anemia, a condition in which there are low numbers of red blood cells and too little hemoglobin.
Hemostatics are used to help the blood clot. There are several types of drugs that function as hemostatics. Lyophilized concentrates are applied to the skin or to a particular area to help control capillary (small blood vessel) bleeding. These products are normally absorbed by the body. Astringents are used directly at the site of bleeding to control bleeding. They constrict the blood vessels and tissue to help slow and stop the blood flow. Epinephrine and norepinephrine are used to constrict the blood vessels and decrease blood flow to the tissues. They may be included in topical medications or applied up the nasal passage in tampons to help decrease and stop nosebleeds. Systemic hemostatics include fresh blood or blood components that are given to animals that cannot clot correctly.
Blood clots can be a serious problem. They can cause strokes or circulation problems and can block blood flow to vital organs. Anticoagulant drugs are used to stop or minimize the clotting process, usually by inactivating the body's natural clotting factors or increasing the rate at which the body dissolves clots.
Drugs Used for Prevention and Treatment of Heartworms
Several macrolide drugs (ivermectin, milbemycin oxime, moxidectin, and selamectin) can be given to prevent heartworm infection in dogs. Macrolides can also be used as preventives in cats. For dogs infected with heartworms, melarsomine dihydrochloride is the only available drug to kill the adult worms. Ivermectin can be used to kill microfilariae and immature heartworms, before giving melarsomine. Macrolides can also be prescribed to treat microfilariae in infected dogs, although they are not approved by the US Food and Drug Administration for this purpose.
Last full review/revision July 2011 by Philip T. Reeves, BVSc, PhD, FACVSc; Jörg M. Steiner, DrMedVet, PhD, DACVIM, DECVIM-CA; Dawn Merton Boothe, DVM, PhD, DACVIM, DACVCP; Maya M. Scott, BS, DVM; Ian Tizard, BVMS, PhD, DACVM; Jozef Vercruysse, DVM, DEVPC