ed on lightly anesthetized mice, as described previously. A small number of animals appeared to have more severe bradycardia in response anesthesia, and these animals were not included in the analysis of the echocardiograhy results to avoid non-specific ” rate-related changes. Briefly, the heart was visualized in the long axis parasternal view for M-mode left ventricle dimension measurement and posterior wall pulse wave tissue Doppler measurement. An apical 4- to 5-chamber view was obtained from the subcostal view for diastolic function assessment with pulse wave spectral LV inflow and outflow and for pulse wave tissue Doppler measurement of the mitral annulus velocities. Relative wall thickness was calculated as /LV EDD. Methods Ethics Statement This study conforms to European Union Council Directives regarding the care and use of laboratory animals, and the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health. Histochemistry and Quantification of Non-Vascular Collagen Following intra-aortic perfusion with phosphate-buffered saline, hearts were excised from mice anesthetized with pentobarbital and fixed in 10% neutral buffered formalin. Fixed hearts were transected perpendicular to the long axis through the ventricles at their widest point and processed routinely for paraffin sectioning. Both portions were embedded so that sections contained 2 cross sections. Sections were cut 5 mm thick and stained with hematoxylin and eosin or Pirosirius Red. Fields of the anterior, posterior and lateral left ventricle and the intraventricular septum were digitally photographed at 10x objective magnification with routine transmitted light and with polarization. For each field, myocardial area was determined by extraction of the green color channel, thresholding, and measurement with Image Pro Plus 6.2 software. Myocardial collagen was determined by inverting polarized images, thresholding, deleting normal perivascular collagenous tissue and measurement of remaining areas. Collagen area was expressed as a percentage of the total myocardial area for each field. Myocyte diameters were measured perpendicular to the long axis of the sarcomeres from unbranched areas of the 
myocytes near an intercalated disk. Animal Model Breeding pairs of the Fabry KO mouse were obtained from the National Institutes of Health. This model as been previously used by Eitzman et al. to analyze vascular function. Control WT animals were gender- and age-matched C57BL/6J mice obtained from the Charles River Laboratories. Male animals were used, and mice were provided standard chow and drank tap water ad libitum. Blood Pressure, Electrocardiography and Echocardiography Measurements 10945827” Systolic blood pressure on trained conscious mice was measured by tail cuff plethysmography using a BQ 123 chemical information BP2000 Visitech model as published previously. Conscious heart rate was extracted from the pulse signal. Electrocardiograms were recorded over a 10 min period in 34-month-old mice under light anesthesia with isoflurane. Arrhythmia was detected by analysis of the tachogram of the recording. Tachograms were constructed from automatic R wave detection and RR plotted against time. All abnormal RR intervals were checked for validation and labeling. ECG intervals were measured from short recordings on average beats, constructed from 200 consecutive QRST complexes. Intervals were determined semi-automatically from a library of QRST waveforms sampled from the tracing. A
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