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The apex of the heart is lowest tip of the organ that points downward at the base, forming what almost looks like a rounded point. “Apex” is a Latin word meaning “summit” or “peak,” and this part of the heart can be thought of in those terms, too. It’s formed mostly by the left ventricle and extends pretty far out to the left in most people. The muscle fibers in this part of the heart are primarily responsible for regulating ventricle contraction, and also play an important role when it comes to relaying and transmitting signals from atrial nodes. Medical professionals often pay particular attention to this peak during physical exams, too. It can be a good place to listen to the beating of the heart since its location often offers clarity without a lot of competing noise, for instance, and it’s one of the four most common heart listening areas. Signals that aren’t coming through the apex as strongly or as frequently as they once did may also be an early sign of heart enlargement or failure.
The main job of the apex from a physiological standpoint is to cause the heart’s ventricles to contract from the bottom up. This provides the driving force that sends the blood up and out of the heart. In most cases this efficiency is the result of the combined efforts of a range of atrial nodes and signal fibers, and the shape of the heart, particularly the way the apex is formed in the left ventricle, is also useful when it comes to acting as a conductor. Signals can quickly go down and around at the peak, and can exit as quickly as they entered.
Regulating the contractions of the ventricles so they are well-timed to the contractions of the atrium is really important to heart health and overall health, too — but the process isn’t always as easy as it might seem. The timing is the result of a system of fibers that runs from the top of the atrium to the apex, where the fibers break into two pathways leading to the left and right ventricles. These fibers found within the walls of the heart are known as Purkinje fibers.
The function of Purkinje fibers is to conduct impulses rapidly. They are arranged within the heart and contract to make the heart’s rhythm most efficient. The fibers work together with a few nodes to stimulate and regulate the impulses.
The sinoatrial (SA) nodes are areas of the heart's atrium that act as the heart's pacemaker. Impulses from the SA node cause the heart’s chambers to contract. Purkinje fibers receive their impulses from the SA node and move the impulse through the heart’s muscles.
Just below the atrium is another node, the atrioventricular (AV) node, which slows the impulses from the SA node. This slower signal proceeds to the apex of the heart and then around to the left and right ventricles. The timing of the impulses from the SA node to the AV node and on to the ventricles is ideally perfect for the flow of blood. Once the blood has reached the ventricles, the Purkinje fibers signal for these spaces to contract.
The heart sits more on the left side of the body than on the right side in most people, and locating the apex usually starts by identifying just where the heart begins and ends. In most people the peak point is somewhere in the vicinity of the fifth intercostal space. The numbering of intercostal spaces — basically the space between two ribs — is done according to the upper rib, so the fifth intercostal space is between the fourth and fifth ribs. The apex is found at this level and typically around 3 to 3.5 inches (8 to 9 cm) from the sternum.
The apex is one of four primary “listening places” for physicians and other caregivers, alongside the second right and left intercostal spaces and the fourth left intercostal space. It’s often believed that the heart’s beating can be best heard here, and there’s also a clarity in these spaces that can help care providers identify problems like murmurs and irregular beats more quickly.
Irregularities in the way the apex directs signals can also be an early warning sign for heart disease. Heart impulses can’t usually be detected simply by listening with a stethoscope, but a heart scan or electrocardiograph (ECG) scan will usually pick them up. When the apex isn’t emitting the same signals as it used to, it can indicate heart enlargement or early failure. Both of these are usually treatable, but the sooner they’re identified the better.