CONDITION
Ventricular Septal Defect
A ventricular septal defect is an opening in the wall that normally separates the two lower chambers of the heart. In a healthy heart, the left and right ventricles are fully divided, allowing oxygen-rich and oxygen-poor blood to flow through separate circuits. When an opening exists, blood can move between these chambers in a way that alters the usual flow. Many owners first become aware of the possibility when a heart murmur is heard during a routine examination, often in a young puppy or kitten. Some animals show no outward signs at all, while others may tire more easily during play, breathe more rapidly than expected, or grow at a slower pace than their littermates. The pattern often depends on the size of the opening and the direction and volume of blood moving through it. This page explores what an owner may observe, the underlying changes in heart structure and flow, the investigations that help characterise the defect, and the range of approaches that may be considered depending on the individual animal and the nature of the opening.
Why this matters now
Ventricular septal defects are present from birth, reflecting a developmental variation in how the heart forms during the earliest weeks of life. The opening is often detected during puppy or kitten health checks in the first few months, though smaller defects may go unnoticed until later routine examinations. Certain breeds, including English Springer Spaniels, English Bulldogs, and West Highland White Terriers in dogs, and Siamese cats, appear to show the condition more frequently than others, suggesting an inherited component in some lines.
The size of the opening itself does not change after birth, but the consequences of that opening can evolve as the animal grows and the demands on the heart shift. Small defects may remain functionally silent throughout life, with no observable effect on activity or wellbeing. Larger openings can lead to progressive changes in heart chamber size and pressure over months to years, as the heart adapts to the altered flow of blood. Some animals remain stable for long periods, while others may develop signs of strain or fluid accumulation as the heart's compensatory mechanisms reach their limits.
Signals & patterns
Early signals
Heart murmur on examination
A murmur is often the first clue, heard by a veterinary surgeon during a routine check or vaccination visit. The sound reflects turbulent blood flow through the opening, and its character can vary depending on the size and location of the defect.
Tiring during play
Some young animals may show less stamina than their siblings, resting more frequently during active periods or choosing to stop sooner. This can reflect the heart working harder to meet the body's oxygen needs when flow is redirected through the defect.
Faster breathing at rest
An increased respiratory rate while calm or sleeping may be noticed, particularly if the defect is allowing a significant volume of blood to recirculate through the lungs. Owners may observe the chest rising and falling more rapidly than expected for a relaxed animal.
Slower growth compared to littermates
In some cases, a puppy or kitten with a larger defect may gain weight more slowly or appear smaller than siblings of the same age. The body may be diverting energy to compensate for inefficient circulation rather than supporting typical growth.
Later signals
Reduced tolerance for activity
As the heart enlarges or pressure changes accumulate, an animal that was once active may begin to avoid exercise or show reluctance to climb stairs or play. The gap between effort and rest may narrow over time.
Coughing or laboured breathing
Fluid may begin to accumulate in or around the lungs if the left side of the heart struggles to manage the increased volume of blood returning from the defect. This can present as a soft cough or heavier, more effortful breathing, particularly after exertion or when lying down.
Abdominal swelling
In some animals, pressure changes affecting the right side of the heart can lead to fluid collecting in the abdomen. Owners may notice the belly appearing rounder or fuller, and the animal may seem less comfortable when touched in that area.
Click to read about the biological mechanisms
How this is usually investigated
Options & trade-offs
Last reviewed: Invalid Date ·