296
3754147819011156112
The1205596012886155218
cardiac1458596012866128175244284346408
cycle1901596012865135196235298
refers2234596012850112159221268323
to2593596012842111
the2740596012842112175
sequence2950596012858119190259322391454516
of3501596012873120
events3655596012865135198269307361
that4052596012842112174213
occur4301596012872135197266313
and4649596012866135205
repeat4889596012850113183245307346
with52745960128101140178248
every851839012862133195242312
heartbeat.1197839012872135197244282352415476515551
It178383901284986
can1905839012864127196
be2136839012872135
divided2306839012871110180219289351421
into2763839012840110149219
23017839012872
major31278390128109170209279326
phases:3488839012872142205258321375414
systole3937839012857128180220289328391
and4363839012864133204
diastole,4602839012871111172227266335375437473
each5110839012864126187257
of5403839012871117
which85110800128101171210273342
subdivides12291080012854124193264302372411481544597
into18621080012839108148217
several21151080012854119188250297358397
smaller25481080012853163223262301364411
phases.29941080012870139202256318373409
Systole12051321012878148201241311351413
and165213210128104174244
diastole,193213210128110150211266304374413476510
when247713210128143213275346
not285813210128111180220
specified31131321012895165228290328375414476545
otherwise,369313210128112151220283330431470524587622
refer43501321012888149196258305
to46901321012880149
ventricular487513210128112173244282329367430499538601647
contraction8511563012862133202242289351412451490559630
and15171563012862131200
relaxation,17531563012847109148210280342381420490559595
respectively.23831563012846108163233295358396434505568605676709
Reminders:12051804012894156265302372443506553607646
10652136012865
Blood12052136012894133203273343
flows1583213601284786155257311
from1930213601284693162272
higher22342136012870110180250313360
to26292136012839108
lower27732136012837108209271318
pressure.31252136012870117179233288358405467502
10652387012865
Contraction12052387012894164233273320382444483521592661
increases19022387012840109172219280342397459513
the24502387012840110173
pressure26582387012871117180234288358405468
within316123870128102140180249288358
a35552387012863
chamber,36522387012863133196305373436483518
while420523870128102171211250313
relaxation45532387012848110148211285346385425494564
lowers51532387012839109211273319373
the8512630012839110172
pressure.10572630012870117180233287358405466501
10652880012865
AV120528800128101202
valves14422880012883145184254317371
open18492880012882152214283
when218128800128101171233302
atrial25192880012875114160199262300
pressures28552880012881128191244299369416478532
are34222880012876122185
higher36412880012883122192262324371
than40472880012851121184253
ventricular43362880012881144213253300338401470508571618
pressures49892880012882129191245300369416478531
and8513123012862133202
close10893123012862101170225287
when141131230128102171234303
the17493123012839109171
pressure19543123012870117179233289358405468
gradient24553123012871118180249288350421459
is2950312301283992
reversed.30783123012846109178239286341404473508
Similarly,12053464012878117227263303366412451522555
semilunar17963464012861123234270310380450513560
valves23913464012875138177247310363
open27903464012877146209278
when311034640128102171234303
ventricular34493464012877139209248295333396465504566613
pressures40973464012877124187240294365412473528
are46603464012869116177
higher48733464012877116186256318365
than52733464012846115178247
aortic/pulmonary8513705012862133180218257320358428498537646714785847894964
pressures,18493705012870117179234289359406468522557
and24433705012862132202
close26803705012862100171225288
when300337050128101170232301
the33403705012839108171
reverse35463705012847109178241287341404
is3985370501283993
true.4113370501283985155218253
The12053947012886155218
cycle14583947012869140200239302
is17953947012846100
initiated19313947012845115155193232294333395465
with243839470128101139179249
the27223947012846115178
firing2935394701285492139178248317
of32883947012877123
the34463947012846115177
SA36583947012885187
node38793947012877148217280
that41943947012845116177216
stimulates44463947012860100138248315355418457518573
the50553947012844115177
atria52673947012869108154193255
to8514189012839110
depolarize.9964189012888151220289329392438476539601636
This166841890128104172212266
is19694189012857111
represented21154189012866128197245307360423492532594664
by28144189012888158
the30064189012858128191
P-wave32324189012896147248310380443
on37104189012888159
the39034189012858128190
ECG.412841890128105198299334
Atrial449641890128120158205244307345
contraction48774189012881150219259306368430469507577647
starts851443001285594157202241296
shortly11824430012869139209256294333404
after16194430012878125164226273
the19264430012854124186
P-wave21474430012893142243305375437
begins,26194430012884147217256325380416
and30704430012876146216
causes33214430012878140209263326381
the37364430012854124187
pressure39584430012884131194247304374421483
within449044300128101140179249288358
the48834430012853123186
atria51044430012877115162200263
to54024430012853123
increase,8514671012839110172218280343396459494
forcing13804671012893162210272310380450
blood186646710128115154224295364
into22664671012884155193263
the25644671012886155218
ventricles.281746710128116178247286333372434473536589625
Atrial347746710128147186233271333373
contraction,388446710128109179249287334397459497535606676711
however,463046710128115186288350419481528563
only522846710128116185225295
accounts8514913012862125187257327397436490
for13774913012847116163
a15754913012864
fraction1674491301284794156218257295366436
of21454913012871118
ventricular22984913012870133202241288327390459497560607
filling,2940491301284785125163202272342377
because33534913012870133194256327381444
at38324913012863101
this39684913012839110149203
point,42074913012870140179249288324
the45664913012838109172
ventricles47734913012870132202240287326388427490543
are53524913012863108170
already8515155012862101149211273342413
almost12975155012865104215282337377
full17095155012849119158196
due19415155012872142204
to21805155012841111
passive23275155012872135188243282352414
blood27765155012872112181251322
flow3133515501284987156258
down34265155012872142244313
the37745155012841112174
ventricles39835155012872135204243290328391435496551
through45705155012841110157228297367438
the50435155012841111173
open52525155012871141204273
AV85153960128101202
valves.10885396012874137176246308362397
As152553960128101155
atrial17165396012866104151189252291
contraction20425396012865135205244292354415454493562633
completes,27105396012866136246314353416454517570606
atrial33515396012866105151190253291
pressure36785396012873120183236291361408470
begins41825396012875138207245315370
to45875396012843112
fall,47355396012851113151191226
reversing49965396012850112182244291346384454524
the8515637012839110172
pressure10575637012870117180233287358405466
gradient15585637012871117180249288350421459
across20535637012860123170240294349
the24385637012837107169
AV264356370128101201
valves,28795637012870132172242304358393
causing33065637012862125195249288358428
them37705637012837108170279
to40825637012839109
close.42275637012862101171226287322
Auscultation120558840126101179233296374413461530577615684763
of20035884012670117
Heart215558840126109170240302349
Sounds.25405884012678148226305383436472
The12056121012886155218
closing14586121012872110180234273344413
of19076121012878125
the20676121012847117180
AV229161210128101201
valves25266121012880143182251314367
produces29296121012878125194265335397460513
the34786121012847116178
first3691612101285695143196235
heart39616121012878141203250292
sound,42896121012862133203272343378
S1,47036121012886155191
and49296121012871140211
marks518461210128109169215286341
the8516362012839110172
beginning10576362012886149219257327397436506576
of16686362012886133
systole.18366362012869140193232303342405440
At232663620128102140
this25026362012854124163217
point,27556362012885155194264302338
ventricular31286362012886148217256303341404473513574621
depolarization,37846362012886148218288327389436474537599637676745816851
represented46696362012863125194242304357420490529592661
by53656362012886156
the8516603012839110172
QRS106566030128102195273
complex,13736603012869138248315355418488524
is1932660301284599
half20676603012876138177224
way233266030128102164234
through,25996603012846117164234305374444479
and31146603012868139208
the33586603012845115178
ventricles35716603012877139209247295333395434496551
start41576603012862100163210248
to44406603012845115
contract,45916603012869138208247294357418457492
rapidly51196603012853115184223293332402
building8516845012870141179219288327397467
up13546845012881151
pressures15416845012881127190244298368415478531
inside21076845012850121175214284347
the24896845012850120183
ventricles.For27076845012881143213252299337400439501555591667738785
a35276845012874
moment,364868450128109177288348418457493
however,41766845012881152254316385447494534
the47456845012850120183
semilunar49636845012866128237274313384455517563
valves8517087012870133172242304358
remain12447087012855117227287326396
closed,16767087012870108179233296365400
and21107087012870140211
the23577087012845115178
ventricles25707087012878140210248296334396435497552
contract31577087012871140209249296357420459
within365970870128102139178248287357
a40527087012870
closed41577087012870108178233296365
space.This45567087012863134196258320355441510549604
phase51957087012877148210264326
is851732801283994
referred9817328012892153200262309355418487
to15047328012883153
as169373280128106161
isovolumetric18897328012883138208279348387457567627666713752815
contraction,273973280128108177246286333394456495534605674710
because348473280128115177239301371426487
no400673280128116186
blood422773280128114154223293364
is46267328012883137
ejected479973280128107146208270309371441
and527673280128106175245
ventricular8517570012870133202241289327389458498560606
volume14927570012871140179249359419
is1946757001283993
unchanged.20757570012871141203273336405475537607642