| heart muscle | <anatomy> Tissue specialised for contraction. See twitch muscle, catch muscle: Cardiac muscle (heart muscle) is a striated but involuntary muscle responsible for the pumping activity of the vertebrate heart. The individual muscle cells are joined through a junctional complex known as the intercalated disc and are not fused together into multinucleate structures as they are in skeletal muscle. Skeletal muscle is a rather non-specific term usually applied to the striated muscle of vertebrates that is under voluntary control. The muscle fibres are syncytial and contain myofibrils, tandem arrays of sarcomeres. Smooth muscle is muscle tissue in vertebrates made up from long tapering cells that may be anything from 20-500m long. Smooth muscle is generally involuntary and differs from striated muscle in the much higher actin/myosin ratio, the absence of conspicuous sarcomeres and the ability to contract to a much smaller fraction of its resting length. Smooth muscle cells are found particularly in blood vessel walls, surrounding the intestine (especially the gizzard in birds) and in the uterus. The contractile system and its control resemble those of motile tissue cells (for example fibroblasts, leucocytes) and antibodies against smooth muscle myosin will cross react with myosin from tissue cells, whereas antibodies against skeletal muscle myosin will not. See: dense bodies. (18 Nov 1997) |
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| heart position | A description of the heart's assumed electrical habitus based upon the form of the QRS complexes in leads aVL, aVF, V1, and V6. Sometimes loosely (and inaccurately) used to describe the frontal plane electric axis. Synonym: heart position. (05 Mar 2000) |
| heart rate | The number of beats per minute. Normal resting heart rates are variable with age, sex, size and overall cardiovascular condition. Heart rate can be determined by taking the pulse. Normal heart rate for an average sized adult is in the range of 60-85 beats/minute. (27 Sep 1997) |
| heart rate, foetal | The heart rate of the foetus. The normal range at term is between 120 and 160 beats per minute. (12 Dec 1998) |
| heart-robbing | 1. Depriving of thought; ecstatic. "Heart-robbing gladness." 2. Stealing the heart or affections; winning. Source: Websters Dictionary (01 Mar 1998) |
| heart sac | <anatomy> A double membranous sac which envelops and protects the heart. The layer in contact with the heart is referred to as the visceral layer, the outer layer in contact with surrounding organs is the parietal pericardium. In between the two layers is the pericardial space. (27 Sep 1997) |
| heart's-ease | 1. Ease of heart; peace or tranquillity of mind or feeling. 2. <botany> A species of violet (Viola tricolour); called also pansy. Source: Websters Dictionary (01 Mar 1998) |
| heart septal defects | Defects in the cardiac septa, resulting in abnormal communications between the opposite chambers of the heart. (12 Dec 1998) |
| heart septal defects, atrial | Defects in the septum between the atria of the heart, due to failure of fusion between either the septum secundum or the septum primum and the endocardial cushions. (12 Dec 1998) |
| heart septal defects, ventricular | Congenital defects in the septum between the cardiac ventricles, most often due to failure of the bulbar septum to completely close the interventricular foramen. (12 Dec 1998) |
| heart septum | The thin membranous structure between the two heart atria or the thick muscular structure between the two heart ventricles. (12 Dec 1998) |
| heart-shaped pelvis | Cordiform pelvis, a pelvis with sacrum projecting forward between the ilia, giving to the brim a heart shape. Synonym: heart-shaped pelvis. (05 Mar 2000) |
| heart-shaped uterus | An incomplete uterus bicornis with a wedge-shaped depression at the fundus. Synonym: heart-shaped uterus, uterus cordiformis. (05 Mar 2000) |
| heart sounds | The sounds heard over the cardiac region produced by the functioning of the heart. There are four distinct sounds: the first occurs at the beginning of systole and is heard as a "lubb" sound; the second is produced by the closing of the aortic and pulmonary valves and is heard as a "dupp" sound; the third is produced by vibrations of the ventricular walls when suddenly distended by the rush of blood from the atria; and the fourth is produced by atrial contraction and ventricular filling but is rarely audible in the normal heart. The physiological concept of heart sounds is differentiated from the pathological heart murmurs. (12 Dec 1998) |
| heart-spoon | A part of the breastbone. "He feeleth through the herte-spon the pricke." (Chaucer) Source: Websters Dictionary (01 Mar 1998) |